Chemistry
Phenobarbital (5-ethyl-5-phenylbarbituric acid or 5-ethyl-5-phenylhexahydropyrimindin-2,4,6-trione) has been synthesized in several different ways.
- Bayer & Co., DE 247952 (1911).
- M.T. Inman, W.P. Bitler, U.S. Patent 2,358,072 (1944).
- Chamberlain, J. S.; Chap, J. J.; Doyle, J. E.; Spaulding, L. B. (1935). Journal of the American Chemical Society 57 (2): 352. doi:10.1021/ja01305a036. edit
- Pinhey, J (1980). "The α-arylation of derivatives of malonic acid with aryllead triacetates. New syntheses of ibuprofen and phenobarbital". Tetrahedron Letters 21: 965. doi:10.1016/S0040-4039(00)77752-5. edit
There is no major difference between them.
The first method consists of ethanolysis of benzyl cyanide in the presence of acid, giving phenylacetic acid ethyl ester, the methylene group of which undergoes acylation using diethyloxalate, giving diethyl ester of phenyloxobutandioic acid, which upon heating easily loses carbon oxide and turns into phenylmalonic ester. Alkylation of the obtained product using ethyl bromide in the presence of sodium ethoxide leads to the formation of α-phenyl-α- ethylmalonic ester, the condensation of which with urea gives phenobarbital.
Another method of phenobarbital synthesis starts with condensation of benzyl cyanide with diethylcarbonate in the presence of sodium ethoxide to give α-phenylcyanoacetic ester. Alkylation of the ester using ethyl bromide gives α-phenyl-α-ethylcyanoacetic ester, which is further converted into the 4-iminoderivative upon treatment with urea. Acidic hydrolysis of the resulting product gives phenobarbital.
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