While both water-soluble (sodium ascorbyl phosphate, magnesium ascorbyl phosphate and ascorbyl glucoside) and oil soluble ascorbyl esters are widely used in cosmetic and therapeutic preparations, one of the most popular forms today is tetrahexyldecyl ascorbate (THDC, VitaSynol® C).
As an oil-soluble derivative, THDC not only improves chemical stability, but its lipophilic nature facilitates delivery into the epidermis and dermis where it undergoes intracellular enzymatic conversion to free ascorbic acid (AA). Importantly, free AA must be released by THDC before its skin benefits can be realized. Thus, THDC is a precursor of AA.
While for 25 years THDC (CAS # 183476-82-6) and Ascorbyl Tetraisopalmitate (CAS #327594-27-4) were construed as being equivalent structures, in fact, they represent two different chemistries with different CAS#s. While both are esters of ascorbic acid, THDC comes from reaction with 2-hexyldecanoic acid whereas Ascorbyl Tetraisopalmitates derives from reaction with isopalmitic acid. Two different fatty acids that when esterified with ascorbic acid yield two unique products.
This misnomer was finally corrected by Sytheon working in close collaboration with the Personal Care Product Council (PCPC) and the Chemical Abstract Services (CAS #provider). Recently, Sytheon has also demonstrated that stability of THDC under an oxidant rich environment and its skin benefits can be improved by combining it with Synoxyl® AZ (INCI: Acetyl Zingerone). This work was published in the International J Molecular Sciences, 22: 8756, 2021, Open access.
Check with your suppliers if you are using the correct INCI name and CAS # for the Vitamin C esters present in your formulation.
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