Preparations of Particular Methyl-, Dimethyl-, and Vinylpyrazines

To illustrate further the general methods of preparation described above, literature preparations of methyl-, dimethyl- and vinylpyrazine are summarized below. 

2-Methylpyrazine. 2-Methylpyrazine has been prepared by decarboxylation of 2 arboxy-5-methylpyrazine (272), 2,3-dicarboxy-5-methylpyrazine (405, 652), and 2-carboxy-3-methylpyrazine (472) from glucose with 25% aqueous ammonia at 100° (33) by dehydrogenation of 2-methylpiperazine (or Mbutyl-2-methylpiperazine) over copper chromite at elevated temperatures (470, 471) (Section 11.6) and in high yield by dehydrogenation of methylpiperazine over catalysts containing CuO, Cr Os, or MnOi at 350-370° (469). Other catalysts have also been used for this dehydrogenation (471,562). 

23-dimethylpyrazine (472, 562). 2,3-Dimethylpyrazine has also been prepared from diamines and diols over Cu-Cr catalyst at about 400 (390). 

5-dimethylpyrazine (508) and 1,2-propylenediamine and 1,2-propyleneglycol over an alumina catalyst at 400 gave 2,5-dimethylpyrazine and other alkylpyrazines (394). 

6- Dimethylpyrazine. This is produced, in addition to other products, by heating glucose and 25% ammonia at 100 (33), by dehydrogenation (91% yield) of 2,6-dimethylpiperazine over copper chromite at 355-360 (468), and (with other products) from 1,2-propylenediamine and 1,2-propyleneglycol over an alumina catalyst at 400 (394). 

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