KINETICS OF HAIR DISULFIDE BOND REDUCTION 83 Table II Values of K* for DTT Derivatives (HS - CH 2 - CH - CH 2 - CH - CH 2 - SH) I OR OR Compound R K K* DBOC CO2H 3.8 x 10 7 0.26 DTT H 6.8 X 10 -6 1.8 DBOM CH• 1.6 X 10 5 3.2 DERIVATIVES OF DITHIOTHREITOL Two diether derivatives of DTT, dimethoxy DTT (DBOM) and diacetoxy DTT (DBOC), are compared with DTT and DTB in Figure 4. DBOM and DTB are signif- icantly faster than DTT in reducing hair, while DBOC is much slower. Values of K • obtained for these derivatives are given in Table II. 1.0- 0.8- 0.6- 0.4- 0.2- 0.0 Figure 5A. SFTK curves for derivatives of dithiopropanol (HS-CH2 10.0, 22øC. \x. ,. \\",. • \ x. \DP-E3 I i I i 0 10 2o 3o 4o Time (minutes) - CH - I ! 50 60 -SH). 0.5 M, pH DP-E3 R = (CH2CH 2- O)2- CH2CH2-- OH. DP-E1 R = CH2CH2OH. DPOM R = CH 3. DTP R = H.

84 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS DPOV x,x '-.,.,DPOC DTP ...... I I I I I 0 10 20 30 40 50 Time (minutes) Figure 5B. SFTK curves for derivatives of dithiopropanol (HS-CH 2-- CH- CH 2- 10.0, 22øC. OR DPOT R = -- CH 2 QCO2H. DPOC R = CH2CO2H. DPOV R = (CH2)5CO2H. DTP R = H. DPOT 60 SH). 0.5 M, pH Comparison of DTT and DBOM clearly indicates that the two hydroxyl groups on DTT slow its reduction of hair. Replacement of both hydroxyl groups by methoxy groups in DBOM increases K* nearly twofold. Any negative effect of the increased bulk of the two methoxy groups on diffusion appears to be more than compensated for by the decreased polarity and loss of hydrogen bonding capability of DBOM. DBOC is very slow in reducing hair. We would expect the rate of diffusion of this compound into hair to be slow because, in addition to being bulky, the two carboxylic acid groups are negatively charged at pH 10, further hindering penetration through the negatively charged hair surface. DERIVATIVES OF DITHIOPROPANOL SFTK curves for six ether-linked derivatives of DTP are shown in Figures 5A and 5B. Values of K* for these compounds are shown in Table III.