Cresol with soap

Solutions of cresol with soap were early pharmaceutical examples of solubilized systems. Phenol itself is soluble in water to the extent of 7.7 % (w/v), but it has disadvantages the alternatives, cresol, chlorocresol, chloroxylenol, and thymol, are much less soluble in water, and their use as disinfectants has led to the need for formulation in surfactant solutions. 

Lysol, B.P, (Solution of Cresol with Soap) consists of a solution of cresol in a saponaceous solvent, the latter being prepared from a vegetable oil (usually linseed) and caustic alkali. 

Clear soluble fluids. Cresol is a mixture of o-, m- and p-methyl phenol (Fig. 10.7A). Because of its poor solubility, it is solubilized with a soap prepared fiom linseed oil and potassium hydroxide. It forms a clear solution on dilution. This preparation, known as Lysol (Cresol and Soap Solution BP 1968) has been widely used as a general purpose disinfectant but has largely been superseded by less irritant phenolies. 

Solubilization has been used for many years in the formulation of phenolic antiseptic and disinfectant solutions. In the case of Cresol and Soap Solution (Lysol) and Chloroxylenol Solution B.P., soap micelles are used to solubilize the phenolic substances. The soap (anionic surfactant) is formed by reaction of potassium hydroxide with a suitable oil such as linseed oil (in Cresol and Soap Solution) or castor oil (in Chloroxylenol Solution). The solubilizing potential of surfactant solutions for hydrophobic species has also been exploited in the design of cholelitholytic solvents for gallstone dissolution with some limited success. 

Phenolic compounds such as cresol, chloro-cresol, chloroxylenol and thymol are frequently solubilised with soap to form clear solutions which are widely used for disinfection. Solution of Chloroxylenol BP, for example, contains 5% w/v chloroxylenol with terpineol in an alcoholic soap solution. 

If the third substance dissolves in both liquids (and the solubility in each of the liquids is of the same order), the mutual solubility of the liquids will be increased and an upper C.S.T. will be lowered, as is the case when succinic acid or sodium oleate is added to the phenol - water system. A 0 083 molar solution of sodium oleate lowers the C.S.T. by 56 -7° this large effect has been applied industrially in the preparation of the disinfectant sold under the name of Lysol. Mixtures of tar acids (phenol cresols) do not mix completely with water at the ordinary temperature, but the addition of a small amount of soap ( = sodium oleate) lowers the miscibility temperature so that Lysol exists as a clear liquid at the ordinary temperature. 

Many derivatives of phenol are now made by a synthetic process. Homologous series of substituted derivatives have been prepared and tested for antimicrobial activity. A combination of alkyl substitution and halogenation has produced useful derivatives including clorinated phenols which are constituents of a number of proprietary disinfectants. Two ofthe most widely used derivatives are/ -chloro-m-cresol (4-chloro-3-methylphenol, chlorocresol, Fig. 10.7C) which is mostly employed as a preservative at a concentration of 0.1%, and / -chloro-m-xylenol (4-chloro-3,5-dimethylphenol, chloroxylenol. Fig. 10.7C) which is used for skin disinfection, although less than formerly. Chloroxylenol is sparingly soluble in water and must be solubihzed, for example in a suitable soap solution in conjunction with terpineol or pine oil. Its antimicrobial capacity is weak and is reduced by the presence of organic matter. 

Advantage is taken of the above principle in the preparation of well known disinfectant lysol. Lysol is a system of cresols and water. These two components do not mix completely at ordinary temperatures, but the addition of soap to the given mixture-soap is soluble in both cresol and water-lowers the C.S.T. to such an extent that the two components readily mix with one another at ordinary temperature to form homogeneous solution. 

Brown and Kaplan made use of the buffering property of oils in phenol solutions. Their formulation contained up to 95% phenol combined with oils. A patch test behind the ear had to be carried out before the facial peel. If there was skin necrosis, they reduced the strength of the phenol by gradually adding oil in small quantities until the right dose was found for the patient s skin. To increase the strength of the mixture, on the other hand, soap (saponified cresol) was added or the concentration of phenol was increased. 

The oils distilled from tar after the light oils are the phenolic oils. Their main components are the phenols and cresols. Pure phenol or phenolic acid is a powerful antiseptic and disinfectant. Together with the cresols, it is used in the manufacture of antiseptic soaps. It is the starting point in the synthesis of the products shown in Table 2-2. 

It has been pointed out by Dodd that all methods involving steam distillation suffer from the defect that higher homologues distil with difficulty, especially in the presence of fatty acids which lower the vapour pressure of tar acids coiisiderablv. Also care must be exercised when drying cresols water is removed with difficulty at 100 and at higher temperatures volatilisation of phenols may take place. Martin s suggests that serious errors may occur in distillation methods where volatile fatty acids (such as in coconut oil) c rv present, but soap made from this oil is not often used as a vehicle for the B.I Ivsol. 

Where either of these is not available, it is recommended that a mixture of 35, 40 and 25 per cent of o-, w- and -cresols respectively should be used, as this mixture has been found to agree closely with the quality of cresylic acid usually employed in soap manufacture. The standard solution is prepared by dissolving TO g of the cresols in 10 ml of N sodium hydroxide and diluting to 1 litre. When phenol is the ingredient 1 g of phenol is substituted for the 1 g of cresol mentioned above. 

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