The present invention relates to the ring alkylation of aniline or an alkylated aniline derivative.
Aniline is an important building block for rubber chemicals (such as diphenylamine, 4-aminodiphenylamine, mercaptobenzothiazole disulfide), dyes, polyanilines and petroleum additives, and crop chemicals. In applications where good hydrocarbon solubility of the compound is important, it is necessary to introduce hydrocarbon chains onto aniline or alkylated anilines to improve solubility.
The prior art has sought to improve the ring alkylation of aromatic amines such as aniline. For example, U.S. Pat. Nos. 4,740,620 and 4,876,377 disclose selective ring alkylation of aromatic amines to an ortho-alkylated product, using an acidic crystalline molecular sieve and partially dealuminated zeolites, respectively. U.S. Pat. No. 5,081,302 discloses the selective ring alkylation of aniline in the presence of zeolite catalysts to para-alkylaniline.
An ionic liquid consists of inorganic and/or organic cations and anions, and typically has a very low vapor pressure, a wide liquid temperature range, and is non-flammable. Ionic liquids can act as a catalyst and/or solvent, and have been studied for utility as solvents, electrolytes, in separations and in fluid applications such as lubricants. See Holbrey, “Industrial Applications of Ionic Liquids,” Chemistry Today 35 (June 2004); Parkinson, “Ionic Liquids Make an Environmental Splash,” 100 Chemical Engineering Progress 7 (September 2004); and Drake et al., “Structural Effects on the Physical Properties of Ionic Liquids,” Air Force Research Laboratory Report No. AFRL-PR-ED-VG-2003-12 (May 2003).
The use of ionic liquids in Friedel-Crafts alkylation has been discussed in Wilkes, “Friedel-Crafts Reactions in Chloroaluminate Molten Salts,” Molten Salt Chemistry: An Introduction and Selected Applications 405 (Mamantov and Marassi Eds. 1987) and Earle et al., “Organic Synthesis,” Ionic Liquids in Synthesis 174 (Wasserschied & Welton Eds. 2003). However, neither study is directed to ring alkylation of aniline or an aniline derivative.
An object of the invention is to provide an improved synthesis for ring alkylation of aniline or an aniline derivative.
A feature of the invention is the use of an ionic liquid as a solvent and catalyst for the ring alkylation of aniline or an aniline derivative.
An advantage of the invention is that use of an ionic liquid typically permits convenient separation of alkylated aniline(s) and alkylated aniline derivative(s) from the reaction mixture.