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Sulfonamides Partition Coefficient Analysis

In the science of rational drug design, log P value of a compound is important to determine its extent of capability to pass through cell membrane. In determining log P of sulfonamides, Thin-layer Chromatography (TLC), ‘shake-flask’ method and High Performance Liquid Chromatography (HPLC) were used. Chemical purity of an unknown sulfonamide, C26 was determined using HPLC. Straight phase TLC is not suitable in determine the partition coefficient of sulphonamides due to the reason it is unable to relate its partition and retention factor. HPLC was found to be the best method in determining log P as it is a reliable and accurate method widely used in pharmaceutical industries. The Ptrue values obtained for sulfathiazole in pH 1 and pH9 using ‘shake-flask’ method were 1.47 and 3.1859 respectively. The log P value obtained from HPLC for C26 is 3.300 and chemical purity value was 68%.
Sulfonamides are antibacterial drugs used to treat infections caused by microorganisms. Sulfonamide antibiotics target on enzyme dihydropteroate synthase(DHPS) which plays an important role in catalysing the bacterial production. They work by inhibit the activity of DHPS which eventually inhibits the synthesis of folic acid and DNA (Foye et al, 1995). Sulfonamides imitate p-aminobenzoic acid (PABA) and compete for the active site. In this way, bacteria could not multiply as there are insufficient of folates available for their growth. In manufacturing the required sulfonamide(C26), an amine which is known as 4-aminoacetophenone is required to obtain the desired final compound.
Sulfonamides’ relative distribution in an n-octanol/water mixture can be done experimentally by measuring the hydrophobic character of the compound. Partition coefficient, P is one of the most crucial factors in controlling the drug action in biological systems. The partition coefficient is an important measure in predicting the absorption, distribution and elimination of drugs in the body. Not only that, it can be used to relate the biological activity of a drug to it properties. Log P, which is known as octanol-water partition coefficient, is used in rational drug design to measure the hydrophobicity of a compound.
It is important to test the hydrophobic character of a drug as it will affect the extent the drug crosses cell membranes easily. The different substituents on a drug have different hydrophobic character and eventually have different biological activity (Patrick 2009). Hydrophobic compounds have a high P value and vice versa for hydrophilic compounds.
Log P can be measured with different methods. Namely, ‘shake-flask’ method, thin-layer chromatography, and High Partition Liquid Chromatography (HPLC) can be used to measure log P. HPLC and TLC are known to be yielding a hydrophobicity parameter rather than a partition coefficient (Takács-Novák and Avdeef, 1996).
The purpose of this study was to investigate the properties of sulphonamides, especially the hydrophobicity of the compounds. Log P was determined using various methods and the advantages and disadvantages of each method used were investigated. Chemical purity of the compound was investigated using the modern HPLC system.
Experimental Establishing the log P of sulfonamides using TLC
In the separation of sulfonamides, TLC was used to establish the log P of the sulphonamides. Sulfonamide solutions were prepared by dissolving 40mg of sulfonamide in acetone and the solutions were made up to 10mL in a volumetric flask which will give a concentration of 0.4% w/v. Then, each individual sulfonamide solution was transferred to a glass capillary tube. After that, the solutions contained in the glass capillary tube were spotted on a plate with silica coated and aluminium backed size at 12cm – 7cm. The plate was then placed in a chromatographic chamber containing mobile phase butan-1-ol for about 60 minutes. When 75% of the mobile phase moves up the plate, the plate was removed from the chromatographic chamber and the mobile phase front was marked. Hot air was washed to dry the plate and the sulfonamides were visualized under short wave UV and the center of each detected spot was marked. The distances from the spots to the mobile phase front and to the center of the detected spot of each sulfonamides were measured using a ruler. The retention factor, Rf value for each sulfonamides was then calculated by following formula:
Rf = Distance moved by spot
Distance moved by solvent
Exploring the partitioning of sulfonamide under ionising and non-ionising conditions using the ‘shake-flask’ method
A 25µg mL-1 solution in 0.5M NaOH( Solution A) and 10µg mL-1 solution in water(Solution B) were prepared using a stock solution containing 0.02%w/v of sulfonamide in water. A range of calibration standards which contain 2.3, 5, 7.5,10, 12.5, and 15µg mL-1 of sulfonamide in 0.5M NaOH was prepared using Solution A. The maximum absorbance of 1.0774 was determined at the wavelength of 257nm using the 15µg mL-1 standard. The standards’ absorbance was read at the ?max of 1.0774 with NaOH as the blank. A graph of absorbance versus concentration for the sulfonamide was plotted using the readings.
Two partitioning samples were prepared by adding 10ml of Solution B, 10mL 0.1M HCl and 20mL octanol in separating funnel (i) and 10mL of Solution B, 10mL pH 9.0 buffer and 20mL octanol in separating funnel (ii). The funnels were shaken at frequent intervals for 30 minutes so that the layers were separated fully. It is important to make sure the funnels were not shaken too vigorously to avoid an emulsion to be formed. Then, the aqueous layer was carefully run off and 20mL 0.5M NaOH was added using a pipette to the remaining octanol in the funnel. The funnel was shaken again for 5 minutes for separation and the absorbance of the aqueous layer was measured at the ?max of 1.0774. The concentration of the sulfonamides in the 0.5M NaOH was calculated from the calibration curve.
Determination of log P values using HPLC
The sample solution was injected into HPLC (Agilent 1120 Compact LC) with column Zorbax C8 measured at 150 mm X 4.6 mm ID. The wavelength is set at 254 nm, flow rate at 1 mL min-1, temperature at 40oC, and injection volume of 20 µL. The running time of the system is set to be 120 minutes. The ratio of mobile phase used in system is 85:15 (0.1% CH3COOH:MeOH)% v/v.
Chemical Purity Determination
A sample solution of C26 at a concentration of 0.1 mg mL-1 was prepared in a 100mL volumetric flask. 7.2mL of methanol was added to dissolve the sample and mobile phase was added to make up to 100mL. 20µL of the sample solution was injected to the HPLC-DAD system with column C18 Phenomenex Luna 5µ measured at 150 mm X 4.6 mm ID using a single injection mode and the method ‘Chempur 1’. The flow rate of the system was set at 1 mL min-1. The ratio of the mobile phase used in the HPLC system is 85:15 (CH3COOH:MeOH) %v/v.
Results and Discussion The literature values for log P of the sulphonamides were listed in the table above. A graph log Rf versus log P was drawn to compare estimate the extent of partitioning against the literature values of log P. Based on Figure 3, it was noticed that there was no relationship between log Rf and log P as the regression coefficient, R2 value was 0.1017. This small value of R2 of 0.1017 shows that only 10.17% of variation in biological activity was accounted for by the parameters of log P and log Rf (Patrick, 2009). However, R value should not be relied on too much as the value obtained does not take any account of the number of compounds that were involved in the study. This means that a higher value of R2 could be obtained if there were more compounds incorporated in the study.
This could be due to straight phase TLC was used in the experiment. The stationary phase in the experiment is the silica layer which will interact with hydrophilicity of a compound. Sulfonamides are hydrophobic compounds so it is best to apply a stationary phase which will interact with the hydrophobicity property of a compound. To improve the results, reversed phase TLC should be considered in determining log P value which is the main concern of hydrophobicity of a compound. In reversed phase TLC, the silica plate has increased amount of alkyl groups which will enable hydrophobic-hydrophobic interaction between the stationary phase and the compound. It will also increase the time of the compound travelling in the mobile phase.
The advantage of using TLC is that log P of many compounds can be determined on one plate. Small amount of sample is required to undergo TLC process. This method is cheaper compared to other methods in determining log P of the compounds. TLC also has the advantage that all constituents of a sample can be visualised easily, especially under UV light. In contrast, the quantitation from the spots obtained from the plate is not easy as TLC is more suitable for the separation of involatile compounds.
Exploring the partitioning of sulphonamide under ionising and non-ionising conditions using the ‘shake-flask’ method
In shake-flask method, the pKa values are required to calculate the partition coefficient ( Takács-Novák and Avdeef, 1996).
The absorbance value obtained for Funnel (i) is 0.219. The value was substituted in the equation as y to obtain x value which is the concentration of sulfathiazole for in 0.5M NaOH.
To calculate Ptrue from the concentration of the sulfonamide contained in 0.5M NaOH, total amount of drug in organic and aqueous phase, Papp and pH of the buffer are required. The working calculations are as below:
For Funnel (i) in pH 1;
Concentration of sulfonamide in organic phase = 2.9796 µg mL-1
1 mL of the organic phase contained 2.9796 µg of drug, this means that 20 mL of organic phase contained a total of 59.592 µg of sulfonamide.
Total sulfonamide in organic and aqueous phase = 10 mL X 10 µg mL-1
= 100 µg
Total sulfonamide in aqueous phase = 100 µg – 59.592 µg
= 40.408 µg
Papp = [sulfonamide] in organic phase / [sulfonamide] in aqueous phase
= (59.592/20)/(40.408/20)
= 1.47
In this case, Papp depends on pH of the solution.
log D at pH 1 = log P – log [1 10(pH-pKa)]
log Ptrue = log 1.47 log [1 10(1-7.1)]
log Ptrue = 0.16731
Ptrue = 1.47
As for Funnel (ii) in pH 9,
Concentration of sulfonamide in organic phase = 0.1905 µg mL-1
20 mL of organic phase contained a total of 3.81 µg of sulfonamide
Total sulfonamide in aqueous phase = 100 µg – 3.81 µg
= 96.19 µg
Papp = (3.81/20)/(96.19/20)
= 0.039609
log Dat pH 9= log P – log [1 10(pH-pKa)]
log Ptrue = log 0.039609 log [1 10(9-7.1)]
= 0.50323
Ptrue = 3.1859
Papp = Ptrue – funionised
0.039609 = 3.1859 – funionised
funionised = 0.012433
= 1.2433%
Sulfathiazole is a weak sulfonamide with pKa value of 7.1. Therefore, it is significantly ionised within a physiological pH range. In this ‘shake-flask’ method, the effect of ionisation on the Papp of sulfathiazole can be investigated by measuring the amount of sulfathiazole being extracted into octanol (organic phase) from aqueous phase at different pH. In pH 1, it is obviously noticed that Papp = Ptrue which means that the drug is 100% unionised as the funionised = 1. From the calculations made from the experiment, the concentration in octanol layer for acidic medium (pH 1) is 2.9796µg mL-1. As for the alkali medium (pH 9), the concentration in octanol is 0.1905µg mL-1. The concentration difference in different pH is due to ionisation of the drug to form a salt which will eventually change the solubility profile. Papp value in pH 1 is expected to be higher than in pH 9 buffer so it is also expected that the absorbance is higher in acidic medium. There are some human errors occurring when preparing the standards. The standard absorbance is set to be more than 1.0 which is not ideal for absorbance measurements. In order to obtain a more accurate result, the absorbance should be set less than 1.0.
The advantage of ‘shake-flask’ method is that log P can be directly obtained using this method. One of the disadvantages of ‘shake-flask’ method is that it is time consuming to make sure that the aqueous and organic layers are separated fully. This method requires good laboratory skills such as skills in shaking the separating funnels. Separating funnels should be made sure not to be shaken too vigorously to prevent emulsion from forming. Laboratory skill such as running off the bottom layer in the funnels is important to avoid the organic layer from running off together with the aqueous layer.

The equation obtained was y =0.4818x 0.3096.
As C26 is an unknown compound, the log P is unknown too. Therefore, the log P for C26 could be calculated based on the equation obtained.
y=0.4818x 0.3096
1.8998= 0.4818x 0.3096
x= 3.300
Log P value for C26 is 3.300
The data follows a straight line with R2 of 0.8782. This straight line indicates that log k increases with log P. This shows that the retention time( time taken to elute from HPLC column) in HPLC is directly affected by the log P of the compound. The higher value of log P causes the longer time the compound stays in the column due to hydrophobic-hydrophobic interaction.
Sulfadiazine and sulfathiazole have Log P values of 1.3 and -0.4 respectively at specific pH of 7.5. This indicates that the log P values are known as Papp which is affected by the ionisation to form a salt. Papp values changed due to the charge as the compound become ionised. The line of a graph would be severely affected with decreasing values of R2 value if Papp values were used to plot the graph. Therefore, Papp should be converted to Ptrue to ensure the linearity of the graph’s line.
There are problems in obtaining Log P for unknown sulphonamide using the old HPLC model system. I could not get any results even though I have waited for more than two hours. This might due to the reason that C26 is a very hydrophobic compound compared to other sulphonamides. C26 has a Log P of 3.300, therefore it is a very hydrophobic drug. This is proven due to the high retention time of 127.257 obtained from the new model of HPLC system .
Polarity of mobile phase can affect the separation of the compound as the retention in reversed-phase liquid chromatography is regulated by interactions in the mobile phase. Low polarity of mobile phase will increase the retention time of the compound as hydrophobic-hydrophobic interaction in the column longer than expected. In contrast, higher polarity of mobile phase will decrease the retention time of the compound. For instance, retention time and separation factor will decrease if the concentration of methanol is increased. This is due to the increased amount of adsorbed organic compound will cause weakening of hydrophobic interaction between the solute and adsorbent (Ching, 2000).
Improvements could be made to the experiment to improve the results. Repeated measurements such as replicate injections of the same solution can be done to obtain accurate results.
The advantages of HPLC method in determining P is that HPLC requires a small amount of sample which does not necessary to have 100% purity. HPLC is more sensitive in detecting the signals even in a small change of concentration. It is easy to operate and is a reliable system. In contrast, it is expensive compared to TLC and ‘shake-flask’ method. Only one sample can be tested at a HPLC system at a time.
Of all the methods, I think that HPLC method is the best method in determining the log P of sulphonamides. The time taken to prepare the sample for HPLC assay is usually short. HPLC can provide a large number of quantitative and qualitative results with a single analytical run (Vogeser et al, 2008).

X 100%
= X 100%
= 67.9975 %
? 68%
C26 has a chemical purity of 68%. Since C26 is an unknown compound, there is no standard required. The chemical purity value of C26 could not be compared with any literature value due to the fact it is an unknown compound.
The partition coefficient of sulphonamides can be measured by different methods in chemistry laboratory such as TLC, ‘shake-flask’ method, and HPLC. From this experiment, it can be concluded that HPLC is the best method in determining the properties of sulphonamides due to the fact that it advantages in obtaining accurate results.

Soap: History and Production Processes

Soap is integral to our society today, and we find it hard to imagine a time when people were kept sweet-smelling by the action of perfume rather than soap. However, the current widespread use of soap is only a very recent occurrence, despite the fact that it has been made for more than 2500 years. The first recorded manufacture of soap was in 600BC, when Pliny the Elder described its manufacture by the Phonecians from goats tallow and ash, and it was known among the British Celts and throughout the Roman Empire. However, these people used their soap medicinally, and it was not until the second century AD that it was used for cleaning, and not until the nineteenth century that it began to be commonly used in the Western world.
Early this century the first synthetic detergents were manufactured, and these have now taken the place of soap for many applications. Their manufacture is covered briefly in the second
A collection of decorative soaps used for human hygiene purposes. This type of soap is typically found inside hotels.
Soap is an anionic surfactant used in conjunction with water for washing and cleaning that historically comes in solid bars but also in the form of a thick liquid.
Soap, consisting of sodium (soda ash) or potassium (potash) salts of fatty acids is obtained by reacting fat with lye in a process known as saponification. The fats are hydrolyzed by the base, yielding alkali salts of fatty acids (crude soap) and glycerol.
Many cleaning agents today are technically not soaps, but detergents, which are less expensive and easier to manufacture.
History Early history
The earliest recorded evidence of the production of soap-like materials dates back to around 2800 BC in Ancient Babylon.[1] A formula for soap consisting of water, alkali and cassia oil was written on a Babylonian clay tablet around 2200 BC. The Ebers papyrus (Egypt, 1550 BC) indicates that ancient Egyptians bathed regularly and combined animal and vegetable oils with alkaline salts to create a soap-like substance. Egyptian documents mention that a soap-like substance was used in the preparation of wool for weaving.
Roman history
It had been reported that a factory producing soap-like substances was found in the ruins of Pompeii (AD 79). However, this has proven to be a misinterpretation of the survival of some soapy mineral substance,[citation needed] probably soapstone at the Fullonica where it was used for dressing recently cleansed textiles. Unfortunately this error has been repeated widely and can be found in otherwise reputable texts on soap history. The ancient Romans were generally ignorant of soap’s detergent properties, and made use of the strigil to scrape dirt and sweat from the body. The word “soap” (Latin sapo) appears first in a European language in Pliny the Elder’s Historia Naturalis, which discusses the manufacture of soap from tallow and ashes, but the only use he mentions for it is as a pomade for hair; he mentions rather disapprovingly that among the Gauls and Germans men are likelier to use it than women.[2]
A story encountered in some places claims that soap takes its name from a supposed “Mount Sapo” where ancient Romans sacrificed animals. Rain would send a mix of animal tallow and wood ash down the mountain and into the clay soil on the banks of the Tiber. Eventually, women noticed that it was easier to clean clothes with this “soap”. The location of Mount Sapo is unknown, as is the source of the “ancient Roman legend” to which this tale is typically credited.[1] In fact, the Latin word sapo simply means “soap”; it was borrowed from a Celtic or Germanic language, and is cognate with Latin sebum, “tallow”, which appears in Pliny the Elder’s account. Roman animal sacrifices usually burned only the bones and inedible entrails of the sacrificed animals; edible meat and fat from the sacrifices were taken by the humans rather than the gods. Animal sacrifices in the ancient world would not have included enough fat to make much soap. The legend about Mount Sapo is probably apocryphal.
Galen describes soap making using causticised lye and prescribes washing to carry away impurities from the body and clothes[3]. The best soap was German according to Galen; soap from Gaul was second best. This is the first record of true soap as a detergent.
Zosimos of Panopolis c. 300AD describes both soap and soap making.[4]
Muslim history
True soaps made from vegetable oils (such as olive oil), aromatic oils (such as thyme oil) and lye (al-Soda al-Kawia) were first produced by Muslim chemists in the medieval Islamic world.[5] The formula for soap used since then hasn’t changed. From the beginning of the 7th century, soap was produced in Nablus (West Bank, Palestine), Kufa (Iraq) and Basra (Iraq). Soaps, as we know them today, are descendants of historical Arabian Soaps. Arabian Soap was perfumed and colored, some of the soaps were liquid and others were solid. They also had special soap for shaving. It was sold for 3 Dirhams (0.3 Dinars) a piece in 981 AD. The Persian chemist Al-Razi wrote a manuscript on recipes for true soap. A recently discovered manuscript from the 13th century details more recipes for soap making; e.g. take some sesame oil, a sprinkle of potash, alkali and some lime, mix them all together and boil. When cooked, they are poured into molds and left to set, leaving hard soap.
In semi-modern times soap was made by mixing animal fats with lye. Because of the caustic lye, this was a dangerous procedure (perhaps more dangerous than any present-day home activities) which could result in serious chemical burns or even blindness. Before commercially-produced lye (sodium hydroxide) was commonplace, potash, potassium hydroxide, was produced at home from the ashes of a hardwood fire.
Modern history
Castile soap was later produced in Europe from the 16th century. Modern castile soap is still popular, being made exclusively from vegetable oil (as opposed to animal fat). Soap, for example, is based on hemp oil in addition to jojoba oil.
In modern times, the use of soap has become universal in industrialized nations due to a better understanding of the role of hygiene in reducing the population size of pathogenic microorganisms. Manufactured bar soaps first became available in the late nineteenth century, and advertising campaigns in Europe and the United States helped to increase popular awareness of the relationship between cleanliness and health.
Sometimes the absence of oxygen in cold and humid environment allows for corpses to naturally accumulate a soap-like coating, adipocere, as covering the Soap Lady on exhibit in the Mutter Museum.
How soap works Soaps are useful for cleaning because soap molecules attach readily to both nonpolar molecules (such as grease or oil) and polar molecules (such as water). Although grease will normally adhere to skin or clothing, the soap molecules can attach to it as a “handle” and make it easier to rinse away. Applied to a soiled surface, soapy water effectively holds particles in suspension so the whole of it can be rinsed off with clean water.
(fatty end) Â :CH3-(CH2)n – COONa: (water soluble end)
The hydrocarbon (“fatty”) portion dissolves dirt and oils, while the ionic end makes it soluble in water. Therefore, it allows water to remove normally-insoluble matter by emulsification.
Soap making The most popular soapmaking process today is the cold process method, where fats such as olive oil react with lye. Soapmakers sometimes use the melt and pour process, where a premade soap base is melted and poured in individual molds. While some people think that this is not really soap-making, the Hand Crafted Soap Makers Guild considers it a form of soap making or soap crafting. Some soapers also practice other processes, such as the historical hot process, and make special soaps such as clear soap (glycerin soap), which must be made through the melt-and-pour process.
Handmade soap differs from industrial soap in that, usually, an excess of fat is sometimes used to consume the alkali (superfatting), and in that the glycerin is not removed leaving a naturally moisturising soap and not pure detergent. Superfatted soap, soap which contains excess fat, is more skin-friendly than industrial soap; though, if not properly formulated, it can leave users with a “greasy” feel to their skin. Often, emollients such as jojoba oil or shea butter are added ‘at trace’ (the point at which the saponification process is sufficiently advanced that the soap has begun to thicken), after most of the oils have saponified, so that they remain unreacted in the finished soap. Superfatting can also be accomplished through a process called superfat discount, where, instead of putting in extra fats, the soap maker puts in less lye.
Lye Reacting fat with sodium hydroxide will produce a hard soap.
Reacting fat with potassium hydroxide will produce a soap that is either soft or liquid. Historically, the alkali used was potassium hydroxide made from the deliberate burning of vegetation such as bracken, or from wood ashes.
Fat Soap is derived from either vegetable or animal fats. Sodium tallowate, a common ingredient in many soaps, is derived from rendered beef fat. Soap can also be made of vegetable oils, such as palm oil, and the product is typically softer. If soap is made from pure olive oil it may be called Castile soap or Marseille soap. Castile is also sometimes applied to soaps with a mix of oils, but a high percentage of olive oil.
An array of oils and butters are used in the process such as olive, coconut, palm, cocoa butter, hemp oil and shea butter to provide different qualities. For example, olive oil provides mildness in soap; coconut oil provides lots of lather; while coconut and palm oils provide hardness. Sometimes castor oil can also be used as an ebullient. Most common, though, is a combination of coconut, palm, and olive oils.
Process In both cold-process and hot-process soapmaking, heat may be required for saponification.
Cold-process soapmaking takes place at a temperature sufficiently above room temperature to ensure the liquification of the fat being used, and requires that the lye and fat be kept warm after mixing to ensure that the soap is completely saponified.
Unlike cold-processed soap, hot-processed soap can be used right away because lye and fat saponify more quickly at the higher temperatures used in hot-process soapmaking.
Hot-process was used when the purity of lye was unreliable, and can use natural lye solutions such as potash. The main benefit of hot processing is that the exact concentration of the lye solution does not need to be known to perform the process with adequate success.
Cold-process requires exact measurement of lye to fat using saponification charts to ensure that the finished product is mild and skin-friendly. Saponification charts can also be used in hot-process soapmaking, but are not as necessary as in cold-process.
Hot process In the hot-process method, lye and fat are boiled together at 80-100 °C until saponification occurs, which the soapmaker can determine by taste (the bright, distinctive taste of lye disappears once all the lye is saponified) or by eye (the experienced eye can tell when gel stage and full saponification have occurred). After saponification has occurred, the soap is sometimes precipitated from the solution by adding salt, and the excess liquid drained off. The hot, soft soap is then spooned into a mold.
Cold process A cold-process soapmaker first looks up the saponification value of the fats being used on a saponification chart, which is then used to calculate the appropriate amount of lye. Excess unreacted lye in the soap will result in a very high pH and can burn or irritate skin. Not enough lye, and the soap is greasy. Most soap makers formulate their recipes with a 4-10% discount of lye so that all of the lye is reacted and that excess fat is left for skin conditioning benefits.
The lye is dissolved in water. Then oils are heated, or melted if they are solid at room temperature. Once both substances have cooled to approximately 100-110°F (37-43°C), and are no more than 10°F (~5.5°C) apart, they may be combined. This lye-fat mixture is stirred until “trace” (modern-day amateur soapmakers often use a stick blender to speed this process). There are varying levels of trace. Depending on how your additives will affect trace, they may be added at light trace, medium trace or heavy trace. After much stirring, the mixture turns to the consistency of a thin pudding.
Essential oils, fragrance oils, botanicals, herbs, oatmeal or other additives are added at light trace, just as the mixture starts to thicken.
The batch is then poured into molds, kept warm with towels or blankets, and left to continue saponification for 18 to 48 hours. Milk soaps are the exception. They do not require insulation. Insulation may cause the milk to burn. During this time, it is normal for the soap to go through a “gel phase” where the opaque soap will turn somewhat transparent for several hours before turning opaque again. The soap will continue to give off heat for many hours after trace.
After the insulation period the soap is firm enough to be removed from the mold and cut into bars. At this time, it is safe to use the soap since saponification is complete. However, cold-process soaps are typically cured and hardened on a drying rack for 2-6 weeks (depending on initial water content) before use. If using caustic soda it is recommended that the soap is left to cure for at least 4 weeks.
Purification and finishing The common process of purifying soap involves removal of sodium chloride, sodium hydroxide, and glycerol. These components are removed by boiling the crude soap curds in water and re-precipitating the soap with salt.
Most of the water is then removed from the soap. This was traditionally done on a chill roll which produced the soap flakes commonly used in the 1940s and 1950s. This process was superseded by spray dryers and then by vacuum dryers.
The dry soap (approximately 6-12% moisture) is then compacted into small pellets. These pellets are now ready for soap finishing, the process of converting raw soap pellets into a salable product, usually bars.
Soap pellets are combined with fragrances and other materials and blended to homogeneity in an amalgamator (mixer). The mass is then discharged from the mixer into a refiner which, by means of an auger, forces the soap through a fine wire screen. From the refiner the soap passes over a roller mill (French milling or hard milling) in a manner similar to calendering paper or plastic or to making chocolate liquor. The soap is then passed through one or more additional refiners to further plasticize the soap mass. Immediately before extrusion it passes through a vacuum chamber to remove any entrapped air. It is then extruded into a long log or blank, cut to convenient lengths, passed through a metal detector and then stamped into shape in refrigerated tools. The pressed bars are packaged in many ways.
Sand or pumice may be added to produce a scouring soap. This process is most common in creating soaps used for human hygiene. The scouring agents serve to remove dead skin cells from the surface being cleaned. This process is called exfoliation. Many newer materials are used for exfoliating soaps which are effective but do not have the sharp edges and poor size distribution of pumice.
Commercial soap production Until the Industrial Revolution, soap-making was done on a small scale and the product was rough. Andrew Pears started making a high-quality, transparent soap in 1789 in London. With his grandson, Francis Pears, they opened a factory in Isleworth in 1862. William Gossage produced low-price good quality soap from the 1850s. Robert Spear Hudson began manufacturing a soap powder in 1837, initially by grinding the soap with a mortar and pestle. William Hesketh Lever and his brother, James, bought a small soap works in Warrington in 1885 and founded what is still one of the largest soap businesses, now called Unilever. These soap businesses were among the first to employ large scale advertising campaigns.
Detergent Our modern technological solution (since the 1940s) to the soap scum problem is to use SYNTHETIC DETERGENTS which don’t precipitate the mineral salts found in hard water. Some of these synthetic detergents are chemically related to soaps, as they are derived from the same fatty acids used to make soaps. SODIUM LAURYL SULFATE (derived from the fatty acid lauric acid by a series of chemical reactions) is such a detergent. It can be found in _many_ common household products. Sodium lauryl sulfate belongs to a class of detergents referred to as “anionic.” These compounds are especially effective at cleaning fabrics that absorb water readily, such as those made of NATURAL FIBERS, such as COTTON, WOOL AND SILK.
“ORVUS” is a commercial name for sodium lauryl sulfate. It is available at feed stores, which sell it as a shampoo for the manes and tails of show animals. Sodium lauryl sulfate is also packaged as a quilt soap and can be found at suppliers of quilting products.
Sodium lauryl sulfate is a common ingredient of SHAMPOOS, and some persons like to use shampoo for handwashing natural fibers. However, you should be aware that shampoos may contain additional compounds which could cause undesirable results if used for laundering fabric.
Read product labels! In the USA, ingredients are listed on labels in order of decreasing quantities. If you use a shampoo for washing natural fibers, you want to find ingredients that contain the chemical prefix “laur” (from lauric acid). Myristic acid, palmitic acid, and stearic acid are also produced from fats by the action of lye, and are considered excellent soaps. Like lauric acid, they are converted into anionic detergents; therefore, you might also find the forms “myris,” “palm,” and “stear” among the ingredients.
The usual granular laundry detergents are sodium salts of fatty derivatives of aromatic sulfonic acids. They are of the anionic class, with similar cleaning properties to those of sodium lauryl sulfate. Manufacturers have now solved the problems with biodegradability which originally plagued these types of synthetic detergents.
Another class of detergents is referred to as “nonanionic.” These are especially good for cleaning synthetic fabrics, such as polyesters. Most are liquids and produce little foam. You’ll find them (along with anionic detergents) in dishwashing liquids and liquid laundry detergents. The “cationic” detergents, as well as being cleaners, also happen to be effective germicides and are used in antiseptic soaps and mouthwashes. They’re also used in fabric softeners because their positive charges (cations) adhere to many fabrics that normally carry negative electrical charges (anions).
In conclusion, it needs to be emphasized that no one cleaning product is best for everything because of the chemical properties of the fabric being cleaned, and the chemical properties of the detergent.
Composition Detergents, especially those made for use with water, often include different components such as:
Surfactants to ‘cut’ (dissolve) grease and to wet surfaces
Abrasive to scour
Substances to modify pH or to affect performance or stability of other ingredients, acids for descaling or caustics to break down organic compounds
Water softeners to counteract the effect of “hardness” ions on other ingredients
oxidants (oxidizers) for bleaching, disinfection, and breaking down organic compounds
Non-surfactant materials that keep dirt in suspension
Enzymes to digest proteins, fats, or carbohydrates in stains or to modify fabric feel
Ingredients that modify the foaming properties of the cleaning surfactants, to either stabilize or counteract foam
Ingredients to increase or decrease the viscosity of the solution, or to keep other ingredients in solution, in a detergent supplied as a water solution or gel
Ingredients that affect aesthetic properties of the item to be cleaned, or of the detergent itself before or during use, such as optical brighteners, fabric softeners, colors, perfumes, etc.
Ingredients such as corrosion inhibitors to counteract damage to equipment with which the detergent is used
Ingredients to reduce harm or produce benefits to skin, when the detergent is used by bare hand on inanimate objects or used to clean skin
Preservatives to prevent spoilage of other ingredients
Sometimes materials more complicated than mere mixtures of compounds are said to be detergent. For instance, certain foods such as celery are said to be detergent or detersive to teeth.
Types There are several factors that dictate what compositions of detergent should be used, including the material to be cleaned, the apparatus to be used, and tolerance for and type of dirt. For instance, all of the following are used to clean glass. The sheer range of different detergents that can be used demonstrates the importance of context in the selection of an appropriate glass-cleaning agent:
a chromic acid solution-to get glass very clean for certain precision-demanding purposes such as analytical chemistry
a high-foaming mixture of surfactants with low skin irritation-for hand-washing of dishware in a sink or dishpan
any of various non-foaming compositions-for dishware in a dishwashing machine
other surfactant-based compositions-for washing windows with a squeegee, followed by rinsing
an ammonia-containing solution-for cleaning windows with no additional dilution and no rinsing
ethanol or methanol in Windshield washer fluid-used for a vehicle in motion, with no additional dilution
glass contact lens cleaning solutions, which must clean and disinfect without leaving any eye-harming material that would not be easily rinsed off.
Terminology Sometimes the word detergent is used to distinguish a cleaning agent from soap. During the early development of non-soap surfactants as commercial cleaning products, the term syndet, short for synthetic detergent was promoted to indicate the distinction. The term never became popular and is incorrect, because most soap is itself synthesized (from glycerides). The term soapless soap also saw a brief vogue. There is no accurate term for detergents not made of soap other than soapless detergent or non-soap detergent.
Plain water, if used for cleaning, is a detergent. Probably the most widely-used detergents other than water are soaps or mixtures composed chiefly of soaps. However, not all soaps have significant detergency and, although the words “detergent” and “soap” are sometimes used interchangeably, not every detergent is a soap.
The term detergent is sometimes used to refer to any surfactant, even when it is not used for cleaning. This terminology should be avoided as long as the term surfactant itself is available.
History The detergent effects of certain synthetic surfactants were noted in 1913 by A. Reychler, a Belgian chemist. The first commercially available detergent taking advantage of those observations was Nekal,[1] sold in Germany in 1917, to alleviate World War I soap shortages. Detergents were mainly used in industry until World War II. By then new developments and the later conversion of USA aviation fuel plants to produce tetrapropylene, used in household detergents, caused a fast growth of household use, in the late 1940s.[2] In the late 1960s biological detergents, containing enzymes, better suited to dissolved protein stains, such as egg stains, were introduced in the USA by Procter HYPERLINK “