Selective process for the preparation of diphenylmethane diisocyanate precursors
AssigneeArco Chemical Technology, L.P.
InventorsCarmen L. Rodriguez, Edward T. Shawl, Haven S. Kesling, Jr.
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Abstract
A selective process for the preparation of diphenylmethane diisocyanate precursors is disclosed. An alkyl phenylcarbamate or an N,N-dialkyl-N'-phenylurea is reacted with a methylene bis(alkyl carbamate) in the presence of an acid catalyst. The use of a staged addition of phenylcarbamate or phenylurea to the methylene bis(carbamate) and the use of a ramped temperature program are the keys to good selectivity to MDI dimer products.
Claims13
A selective process for making a diphenylmethane dicarbamate, said process comprising:
- (a) slowly adding a mixture of an alkyl phenylcarbamate and an effective amount of an acid to a methylene bis(alkyl carbamate) at a temperature within the range of about 20.degree. C. to about 55.degree. C. to produce an aryl-alkyl dicarbamate;
- and
- (b) heating the aryl-alkyl dicarbamate in the presence of additional alkyl phenylcarbamate at a temperature within the range of about 60.degree. C. to about 100.degree. C. for a time sufficient to produce the diphenylmethane dicarbamate.
A selective process for making a methylene diphenylene dicarbamate, said process comprising:
- (a) slowly adding a mixture of an alkyl phenylcarbamate and an effective amount of a protic acid having a pK.sub.a less than about 0 to a methylene bis(alkyl carbamate) selected from the group consisting of methylene bis(methyl carbamate) and methylene bis(ethyl carbamate) at a temperature within the range of about 20.degree. C. to about 55.degree. C. to produce an aryl-alkyl dicarbamate;
- and
- (b) heating the aryl-alkyl dicarbamate in the presence of about one equivalent of additional alkyl phenylcarbamate at a temperature within the range of about 60.degree. C. to about 100.degree. C. for a time sufficient to produce the methylene diphenylene dicarbamate;
- wherein the molar ratio of alkyl phenylcarbamate to methylene bis(alkyl carbamate) in step (a) is within the range of about 0.8 to about 1.5.
Dependencies are inferred from the claim text.