March 3, 2014
Here’s an improved synthesis of a fiber dye. J. M. Gardlik and co-inventors disclose an improved process for making 2-methoxymethyl-1,4-benzenediamine (5), its derivatives, and its salts. This compound is a component of dyes for keratin fibers.
The inventors state that existing processes for preparing 5 “are not completely satisfactory,” but they do not give any reasons. In their process, the key step is a reductive amination that forms quinone monoxime intermediate 3. The figure shows the route described in the patent.
Starting phenol 1 is methylated by heating it with MeOH under pressure. Ether 2 is isolated as a dark brown oil in 98% yield and is used without purification to synthesize intermediate 3. In this reaction, as acidified 2 is treated with 6 M NaNO2, 6 M H2SO4 is added to maintain the pH at 2.0. The product precipitates from solution as a brown solid in 53% yield.
Compound 3 is treated with HONH2·HCl in the presence of K2CO3 to produce dioxime 4 in quantitative yield and in sufficient purity to be used in the next step. Using an ≈90-fold excess of hydrazine in the presence of Raney nickel converts 4 to 5 in 83% yield. The inventors do not report the purity of 5, but they do provide 1H NMR data for 5 and intermediates 2, 3, and 4.
The inventors also claim the preparation of derivatives and salts of 5, but do not give details. The process’ primary advantage is that it gives a good yield of the desired product and does not require the purification of intermediates. (Proctor & Gamble [Cincinnati]. US Patent 8,592,631, Nov. 26 2013; Keith Turner)