Study On Synthesis-mechanism Of Chloropropanoic And Chloroacetic Acid With Acid Anhydride As Catalyst

α-monochloropropanoic acid and monochloroacetic, which are widely used in pharmaceuticals, pesticides, dyestuff, are active and important organic intermediate in fine chemistry engineering field.The chlorination products of propanoic acid chlorinated with propanoic anhydride as catalyst are α-monochloropropanoic acid, β-monochloropropanoic acid, α,α-dichloropropanoic acid and α,β-dichloropropanoic acid. The chlorination products of acetic acid chlorinated with acetic anhydride as catalyst are monochloroacetic acid, dichloroacetic and trichloroacetic acid. Studying on the synthesis-mechanism of α-monochloropropanoic and monochloroacetic acid has very important application value in process produced of improving yield and purity of main products α-monochloropropanoic acid and monochloroacetic acid.According to the reaction mechanism research of α-monochloropropanoic acid and monochloroacetic acid by predecessors, this test mainly studied the following four parts:The first part, propanoic acid was chlorinated by chlorine with propanoic anhydride and propanoic anhydirde added with concentrated sulphuric acid as catalyst, respectively. Then the comparative analysis of some chlorination product ofα-monochloropropanoic acid, β-monochloropropanoic acid and α,α-dichloropropanoic acid was conducted. The results show that the generated rate of α-monochloropropanoic acid is accelerated in prophase and metaphase of the reaction and the production has increased when concentrated sulphuric acid was added. However,production of β-monochloropropanoic acid and α,α-dichloropropanoic acid has decreased.The second part, in the presence of propanoic anhydride, the generated proceeded of α-monochloropropanoic acid along two routes: the radical and ionic mechanism. The generated proceeded of β-monochloropropanoic acid and α,β-dichloropropanoic acid along radical chlorination mechanism. The generated proceeded ofα,α-dichloropropanoic acid along two routes: the radical and ionic mechanism. The ionic mechanism of α,α-dichloropropanoic acid is divided into parallel route and consecutive route of acid-catalyzed. All above generated routes were calculated by Dmol3 program of Materials Studio 5.5. Transition states of each route were searched and determined its uniqueness, further, reaction activation energy was obtained.Combined with the experimental results, it is concluded that the generated route ofα-monochloropropanoic acid is acid-catalyzed enolization of propanoyl chloride which was the rate-determining step in the ionic mechanism. The generated routes of main byproduct of β-monochloropropanoic and α,α-dichloropropanoic acid areradical mechanism, and the generation of α,α-dichloropropanoic acid mainly via a consecutive radical path, i.e. α-monochloropropanoic acid chlorinated further to it.Secondary byproduct of α,β-dichloropropanoic acid is formed via a consecutive path, i.e. β-monochloropropanoic further radical chlorination.The third part, first of all, acetic acid was chlorinated by chlorine with different amount of acetic anhydride as catalyst. Then the comparative analysis of some chlorination product of monochloroacetic acid and dichloroacetic acid was conducted. The results show that the production of monochloroacetic acid has increased and dichloroacetic acid has decreased along with the increased amount of acetic anhydride. Then, acetic acid was chlorinated by chlorine with acetic anhydride, acetic anhydride added with concentrated sulphuric acid and acetic anhydride added with ferric trichloride as catalyst, respectively. The results show that the generated rate of monochloroacetic acid is accelerated significantly in prophase and metaphase of the reaction and the production has increased when concentrated sulphuric acid or ferric trichloride was added. Also, the production of dichloroacetic acid has increased at the same time.The fourth part, in the presence of acetic anhydride, the generated proceeded of monochloroacetic acid is along two routes: the radical and ionic mechanism. The generated proceeded of byproduct dichloroacetic acid and trichloroacetic acid is along two routes: the radical and ionic mechanism. The ionic mechanism of byproducts is also separated into parallel route and consecutive route of acid-catalyzed.All above generated routes were calculated by Dmol3 program of Materials Studio5.5. Transition states of each route were searched and determined its uniqueness,further, reaction activation energy was obtained. Combined with the experimental results, it is concluded that the generated route of monochloroacetic acid is acidcatalyzed enolization of acetyl chloride which is the rate-determining step in the ionic mechanism. Byproduct of dichloroacetic acid generated mainly via the parallel reaction of generating chloroacetyl chloride. Byproduct of trichloroacetic acid generated mainly via the parallel reaction of generating 1,2-dichloroacetyl chloride.