C-nitrosoaniline compounds and their blends as polymerization inhibitors

A method for inhibiting the premature polymerization of ethylenically unsaturated monomers comprising adding to said monomers an effective amount of at least one inhibitor selected from the group consisting of C-nitrosoaniline compounds of the structure:

• wherein R1 and R2 are independently selected from the group consisting of hydrogen, alkyl, aryl, acyl, hydroxyl, alkoxy, nitroso, and sulfonyl, provided that at least one of R1 and R2 is hydrogen, or R1 and R2 can form a cyclic ring that is aryl, cycloalkyl, polyaryl, or heterocyclic;
• R3 through R7 are independently selected from the group consisting of hydrogen, alkyl, aryl, acyl, hydroxyl, alkoxy, acyloxy, NR8(R9), nitro, nitroso, halogen, and sulfonyl, or any two adjacent R's can form a cyclic ring that is aryl, cycloalkyl, polyaryl, or heterocyclic, provided that at least one of R3 through R7 must be a nitroso group;
• and
• R8 and R9 are independently selected from the group consisting of hydrogen, alkyl, aryl, acyl, and nitroso.

A method for distilling a feed comprising at least one polymerizable ethylenically unsaturated monomer, said method comprising the steps of:

• introducing a feed comprising at least one polymerizable ethylenically unsaturated monomer into a distillation apparatus;
• introducing a polymerization inhibiting effective amount of at least one inhibitor selected from the group consisting of C-nitrosoaniline compounds wherein the aniline moiety of said compounds is a primary or secondary amine into said distillation apparatus;
• and
• distilling said feed under distillation conditions in the presence of said inhibitor to recover from said distillation apparatus an overhead product of high purity ethylenically unsaturated monomer and a residual bottoms fraction having a reduced content of polymeric material.