374 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS BUTYL STEARATE OCTYL DODE•NOL CASTO ERAL OIL! • • '•ø• •'•' • •- •01L I SOSTEAF•ETH--2 CAS INERAL OiL/ •,•o?•-• 'SOIL •0• CETYL A •--ETATE Oll CAS ERAL OIL/ / ,, \OIL C12--15 BENZOATES CAS ERAL OIL! • * •'% ...... XOiL OLEYL ALCOHOL CAS INERAL OIL / /•,.,•o•u•,-,• -'%OIL ISOPROPYL PALMI TATE CAS ERAL OIL/ ,/ • NSI•OLUE:•LI'- XOIL PROPYLENE •LY•--OL D I PELAR•ONATE CAS INERAL OIL/ / ..... ...... \OIL Figure 2. Ternary diagrams of cosolubilizers for castor oil/mineral oil.

COSOLUBILIZERS 3 7 5 Table I Solubility Parameters and Percent Cosolubilizer Required to Solubilize Castor Oil/Mineral Oil (50/50) at 25øC Relative solubilization strength 8 % Required S.P. Cosolubilizer (25) Regress. 6.19 Isocetyl stearate 50.9 56.2 % -- Safflower oil 44.0 -- 6.92 Decyl oleate 40.6 39.5 7.09 Mineral oil -- 7.17 Isodecyl oleate 40.8 34.9 -- Avocado oil 39.0 7.43 Isostearyl neopentanoate 35.1 30.7 -- Glycereth-3 palmitate 34.0 -- Almond oil 32.4 7.44 Octyl palmitate 31.0 30.5 7.87 Olive oil 30.0 24.9 7.68 Butyl stearate 28.0 27.2 7.78 Isopropyl palmitate 28.0 26.0 -- Isodecyl isononanoate 26.5 Pentaerythr. tetraoleate 24.8 8.10 Coconut oil 23.4 22.6 7.63 C x2-C •5 alcohol benzoates 23.0 27.8 8.06 Cetyl acetate 90% 22.5 23.0 8.21 Propylene glycol dipelarg. 22.0 21.6 Eucalyptus oil 22.0 -- 8.29 Caprylic capric triglyceride 21.0 21.0 PPG-2 Myristyl ether 21.0 -- 8.29 Isosteareth-2 (HLB 2.0) 21.0 21.0 Propylene glycol laurate 20.5 -- 8.43 Oleth-2 (HLB 4.9) 19.9 20.0 8.67 Isostearyl alcohol 15.0 18.8 8.71 Isocetyl alcohol 12.7 18.7 8.87 Myristyl lactate 13.1 18.2 8.90 Castor oil -- -- 8.92 Octyl dodecanol 14.5 18.1 8.95 Oleyl alcohol 15.3 18.0 9.00 Linear alcohol lactates 19.2 18.0 9.20 Lauryl lactate 20.5 17.9 9.34 Padimate O 23.6 18.1 10.21 Dioctyl malate 21.6 23.1 10.29 Homosalate 27.2 23.9 regression of cosolubilizer requirements in castor oil dominant systems results in sig- nificantly improved correlation. % Cosol. req = 14.5 spc + 141.2 (r = 0.9725) Figure 3 shows the cohesive interaction increasing as the cosolubilizers become more strongly bound to the castor oil. The single greatest deviant from the regular interaction mean (the straight line in Figure 3) is the C•2-C•5 alcohol benzoates, whose higher cohesion is attributed to exaggerated specific interactions of polar portions of molecules. Thus it exhibits the only "coupling" behavior among the many cosolubilizers we ex- amined.