Paralysis in man and the domestic fowl caused by “ToCP” (tri-cresyl phosphate, tri-tolyl phosphate or TTP) is reviewed, and the search for a non-toxic plasticizer derived either from TTP or tri-xylenyl phosphate (tri-dimethylphenyl phosphate or TXP) is described. It had been previously shown that the ortho-tolyl esters are toxic but we found that their removal does not make the mixture non-toxic. The meta- and para-tolyl esters were known to be free from toxic effects and the 2: 4 and 2: 5 dimethylphenyl esters were equally shown to be non-toxic except in massive doses. We confirmed that the tri-ortho-ethylphenyl ester was non-toxic, but found the mono- and di-ortho-ethylphenyl phosphates to be highly toxic. We showed that TTP made from phenols with all the ortho-cresol and ortho-ethylphenol removed is non-toxic.
With TXP, however, elimination of all ortho-cresol and ortho-ethylphenol from the raw materials does not result in a non-toxic plasticizer. Tri-ortho-n-propylphenyl phosphate was shown to non-toxic but esters containing one or two ortho-propylphenyl groups are toxic.
The toxicity of the ortho-tolyl, ortho-ethylphenyl and ortho-propylphenyl groups is much reduced in the presence of the 3: 5-dimethylphenyl group. This influence is greatest in mono-ortho-propylphenyl-di-3: 5-dimethylphenyl phosphate which is non-toxic in five consecutive daily doses of 500 mg./kg. body weight.
The removal of all ortho-cresol, ortho-ethylphenol and ortho-propylphenol from the raw material results in a non-toxic product which we termed non-toxic plasticizer “NTP”. This has been fed in various doses to a variety of mammals and a large number of chickens in short term tests without toxic effects.
Our experiments showed that tri-meta-ethylphenyl phosphate is non-toxic but tri-para-ethylphenyl phosphate is highly toxic. The mixture from which NTP is made contains 10% of para-ethylphenol. Based on chemical statistics the tri-para-ethylphenyl ester can be present only in minute quantities, and we have shown that esters containing one or two para-ethylphenyl groups are non-toxic. An ester with a methyl group in the ortho, and an ethyl group in the para position in the same benzene nucleus (tri-2-methyl-4-ethylphenyl phosphate) we showed, surprisingly, to be non-toxic.