Methods for Synthesis of an Advantageous N-Heterocyclic Carbene Catalyst
The present invention concerns the synthesis of the salts of a Triazolium N-Heterocyclic Carbene (NHC) catalyst in various salt forms prepared from 2-methylaniline, 2-methylphenylhydrazine hydrochloride or 2-methylphenylhydrazine. The molecules so prepared are useful in catalysis of carbene reactions and are advantageous due to their lack of chlorinated or fluorinated intermediates and lack of chlorine or fluorine in the final structure.
1 . A method for the synthesis of the N-Heterocyclic Carbene catalyst salt of Formula 1, the method comprising: (a) contacting 2-methylaniline with aqueous hydrochloric acid to form the amine chloride; (b) contacting the amine chloride in solution with a diazotization reagent to form the diazonium chloride salt; (c) adding a reducing agent to convert the diazonium chloride salt to 2-methylphenylhydrazine hydrochloride; (d) filtering to recover the 2-methylphenylhydrazine hydrochloride salt as a solid; (e) contacting the recovered 2-methylphenylhydrazine hydrochloride salt with an aqueous base to form free 2-methylphenylhydrazine; (f) extracting the 2-methylphenylhydrazine from the aqueous basic solution with an organic solvent to provide a solution of the 2-methylphenylhydrazine in the organic solvent; (g) drying the solution of 2-methylphenylhydrazine by addition of a drying agent; (h) removing the drying agent by filtration; (i) contacting the dry 2-methylphenylhydrazine solution with the reaction products of 2-pyrrolidine and dimethylsulfate to make iminohydrazone of Formula 2 in an organic solvent; (j) distilling the solution of the iminohydrazone of Formula 2 to remove excess solvents; (k) recovering the iminohydrazone of Formula 2 as a solid salt; (l) contacting the iminohydrazone salt of Formula 2 with an organic solvent and trimethylorthoformate to make methylsulfate salt of the N-Heterocyclic Carbene catalyst of Formula 1; (m) recovering the N-Heterocyclic Carbene catalyst of Formula 1 as a salt.
2 . A method as in claim 1 , wherein the diazotization reagent is sodium nitrite (NaNO2).
3 . A method as in claim 1 , wherein the reducing agent is stannous dichloride.
4 . A method as in claim 1 , wherein the temperature in steps (a), (b) and (c) is maintained locally, where locally means 250 cc volume increments, throughout the reactor between about 0 degrees C. and about 5 degrees C.
5 . A method as in claim 1 , wherein the temperature in step (i) is about 60 degrees C. to about 80 degrees C.
6 . A method as in claim 1 , wherein and the temperature in step (l) is about 80 degrees C. to about 100 degrees C.
7 . A method as in claim 1 , wherein the solvent in steps (f), (i) and (l) is an aromatic hydrocarbon.
8 . A method as in claim 1 , wherein the solvent in steps (f), (i) or (l) is selected from the group of toluene, a mixture of xylenes, m-xylene, o-xylene, p-xylene.
9 . The method of claim 1 , wherein the synthesis begins with step (e) using 2-methylphenylhydrazine hydrochloride.
10 . The method of claim 1 , wherein the synthesis begins with step (i) using 2-methylphenylhydrazine.
11 . The method of claim 1 , wherein tin salts are recovered from the filtrate after step (d) by neutralization with a hydroxide base to produce stannic hydroxide which is subsequently filtered and dried to produce stannic oxide (SnO2) for reprocessing to tin and subsequently to the stannous dichloride.