234 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS Table I 30 Per Cent Indices of Hair Samples Following Treatment wtth Alkyl Iodides Treatment 30 Per Cent Index Intact 0.98 Reduced 0.54 Reduced--CHal 0.66 Reduced--C6H•aI 0.66 Reduced--C•0H2•I 0.64 Table II 30 Per Cent Indices of Wool Samples Following Treatment with Alkyl Iodides Treatment 30 Per Cent Index Intact 1.02 Reduced--CHaI 0.63 Reduced--C•HtaI 0.85 Reduced--C•0H2•I 0.92 /•EC•, TGA O.16 I CHal REMAINING I[ 0.08• 0 20 40 REACTION lIME, min. Figure 1. Reactivity of thioglycolic acid with methyl, ethyl and butyl iodides in 40 per cent ethanol, pH 9 with respect to time The alkylation of the reduced wool with hexyl and decyl iodides resulted in weight gains of 1.7 and 2.5 per cent, respectively. It was obvious that the extent of alkylation was again low. On the basis of the weight gain, only 0.18 to 0.20 m moles at most, of SH per gram of wool had been alkylated. Yet, the mechanical performance of the alkylated wool (Table II) conformed with the earlier data published by Harris. There was a steady improvement in the mechanical recovery of the fibers with the increasing

HYDROPHOBIC BONDS AND HAIR TREATMENTS 235 chain length of the alkylating agent. However, this unexpected discrepancy between the weight gain values and the 30 per cent work indices was resolved satisfactorily by the amino acid analyses of the treated wools. The cystine contents of both hexyl iodide and dec¾1 iodide treated samples were almost identical with those of the untreated unreduced wool (860 /xmol/g). The methyl iodide alkylated sample had a cystine content of 470 /xmol/g. It is, thus, obvious that the mechanical recovery of the alkylated wool fibers had been brought about by reformation of the keratin disulfide and not by the residue reinforcement effect. The mechanism of the disulfide rebuilding is not yet known. Most likely, the alkyl iodides undergo some secondary reactions involving formation of iodine which acts as an oxidant for the protein sulfhydryl. This secondary reaction is unimportant in the case of methyl iodide, which reacts with mer- captans very rapidly. An increase in chain length of the alkyl group causes a precipitous drop in the rate of the alkylation reaction (Fig. 1), and thus, may set a stage for the secondary process. 3. Synthesis ofN-alkyl maleimides: A more dependable method for introducing apolar residues into the keratin was clearly required. N-ethyl maleimide is often used as a standard blocking agent for protein sulfhydryl, and it was thought that its higher homologues might be of value in this respect. Although, the N-alkyl maleimides are not commercially available, they were easily pre- pared by pyrolysis of the corresponding N-alkyl maleamic acids (5, 6). N-hexyl, N- heptyl, and N-dodecyl maleamic acids were prepared by reacting maleic anhydride with the appropriate amine in glacial acetic acid. The acids' were isolated in good yields (ca. 85 per cent) as white crystalline solids and pyrolyzed without further purification. The properties of the maleamic acids and the corresponding maleimides are given in Table III. The low yields of final product (26 per cent) were due to a concurrent poly- merization reaction leading to a resinous by product. In the course of our work, a one step synthesis was also utilized for the preparation of N-alkyl (aryl) maleimides. The overall yield continued, however, to be low (-30 per cent). The overall reaction is showh below CH•H O-•-C C=O + RNH• --,-CH--CO•H N/ o CH--CONHR 170-180 • C. C H-•-C H I O =C C---•O N I R + H20 4. Reduction of hair with dithiothreitol (DTT).' DTT was used as an alternate reductant in our studies. This reagent (8) causes a specific and symmetric scission of the