DISULPHIDES AND MERCAPTANS IN HAIR CHEMISTRY one that excellent non-relaxing ,aves can be obtained without need additional fixing or setting •ses. materials are used in concen- of 3 to 8 per cent, the speed waving increasing with concentra- tion up to 15 per cent. By varying concentration of mercaptan the y practical adjustments of 'waving speeds Car/be made to suit .liferent systems of hot or cold waving as well as different types of air. Treatment can be carried out in aqueous solutions of pH7 up to but not including 10, but in prac- it is found desirable not to pH9'5, otherwise the time .:in which it is possible to wave the is too short. Optimum alka- •:•:,•.• . is pH9'2-9'5. Ifi cold waving ::/•'•/•!i?.i::..,careful pH control is essential, speed ::½ji!( :!øf waving increasing with pH of the •i?.:!?:'thiol solution. 'So far as pH regula- •'?•i•111':tion is concerned McDonough states :'i:i?i:'•'that while all alkaline materials are •,•: :' satisfactory, bases with a dissocia- tion constant less than 5 x 10-' and- ?!?Preferably about 10 -• are much less i?,:}:.destructive in action. For cold i?i'::.'waving, volatile bases such as am- }.?.!•: monia, methylamine or ethylamine :i•!i}:-•:i are preferable to non-volatile alkalis :-:: :• since the former give tighter waves. {?::!Ammonia, in particular, is outstand- ?•!(.ing in its advantages since its odour blends pleasantly with that of ii:'.:i:' mercaptans, the ionisation constant :•:i.. is satisfactory, and between pH 7-10 ß : i::: it is relatively non-irritating to the !::!½: skin. These basic U.S. patents, }i': together with 22 similar patents and : ( .:' patent applications in other coun- ß tries, cover the use of mercaptans in cold waving and have recently resulted in the issue of world-wide licensing agreements. Thioglycollates are the mercap- tans most widely used, and formu- lated with resin dispersions produce cloudy or opaque cold wave prepara- tions. Recently, '* it was suggested that 0'3 to 0'5 per cent lanette wax SX or cetyl alcohol, distilled water and wetting agent (secondary sodium alkyl sulphate or alkyl aryl sodium sulphonate) be emulsified in the usual way and aftei' cooling to room temperature, thioglycollic acid and ammonia be added. Since early in 1949 thioglycerol has been widely used for home waving in France. Prepared as a 20 per cent solution from glycerol monochlorhydrin and sodium hydro- sulphide, it is sold to the public as 5 per cent thioglycerol and 15 per cent ammonia. •' This solution of pH 10'5 gives excellent waves, the setting time being at most 2 hours and even with difficult hair the waves last 6 months? For saloon u•e, however, the speed of waving is too low, and while good results are obtained at high temperatures, liber- ation of h•drogen sulphide makes the process impracticable. Instabil- ity of an. ammoniacal solution of thioglycerol necessitates addition of ammonia to the mercaptan solution immediately before use, which is a further manipulative disadvantage. Morelle TM has, therefore, developed the use of thiolactic acid, formed by reaction of •-chloropropionic acid with sodium hydrosulphide, followed 177

JOURNAL OF THE SOCIETY OF COSMETIC 'CHEMISTS by acidification of the alkaline thiolactate, extraction and distilla- tion. Ammonium thiolactate is claimed to be non-toxic under .nor- mal use, furthermore, it reduces cystine disulphide linkages, but does not give rise to any appreciable fibre swelling, so that damage to the hair is minimal. Finally, it is stated th,at the wave produced has a strikingly natural appearance, and the hair is supple and glossy without the use of auxil/ary agents. In view of the early use of ammon- ium hydrogen sulphide for cold waving it is interesting to note that some two years ago an Austrian patent 3• claimed the use of 5 to 15 per cent monomethanolammon- ium sulphide pH 9-11, followed by a finishing rinse containing an oxidising agent. The reagent is stated to g/re good results with bleached and porous hair, wkile the odour is reported to be less unpleasant than that of the thioglycollates. Informa- tion on .relative toxicity, however, was not given. " Until comparatively recently, cold waxing involved the use of two solutions, the thioglycollate being followed by a "neutraliser" whose function is to remove' excess mer- captan by oxidation to disulphide. At the same time depression of the fibre swelling resulting from treat- ment with thioglycollate occurs to a variable extent, while rebuilding of cross-linkages can increase fibre stability. Where the initial reduc- tion process has caused appreciable modification of the hair it is impor- tant that rinsing should be thor- 178 ough/y carried out in order to allow these last two reactions to occur, otherwise the hair will remain permanently damaged. Solutions of hydrogen peroxide, acidified with organic acids, such as tartaric, citric or acetic have been used, the acid peroxide oxidising the thioglyco]late without bleaching the hair pigment. The amount and nature of the acid used in the oxidising rinses are factors exercising considerable influ- ence on the efficiency of oxidation, citric acid, for example, being an acid to avoid?' A second type of oxidising agent is based on solutions of ammonium, alkali or alkaline earth iodate or bromate, potassium ?. bromate in particular having wide- spread use in home permanent.i. li waving kits. Several cases of acci.- dental or suicidal ingestion of such bromates have drawn attention to the potential dangers of these mater- iaJs, and one manufacturer has replaced bromate by the mu(•h less '::i toxic sodium perborate and sodium?: :' hexametaphosphate. •oketo acids:! pyvic or acids (1'5 to 2 per cent, together withi? a wetting agent) have also been forward as alternative rinses." ' Recently, cold waving solution, S,!':½ii which do not require a "neutraliser•.?i•! have appeared on the British U.S. markets. The method of Beste ii and Reed '• replaces the oxidising•!i! rinse by atmospheric oxidation cata •i ? lysed by soluble salts of manganese.or iron, applied as ai: ? preliminary rinse or in the wavings)! lotion. Advantages claimed for thisii}i process are better control of the:!•i : ':: •