ACADEMIA ROMÂNĂ Rev. Roum. Chim., Revue Roumaine de Chimie 2018, 63(3), 235-244 http://web.icf.ro/rrch/ MECHANISM OF CHLORINATION PROCESS: FROM ACETIC ACID TO MONOCHLOROACETIC ACID AND BYPRODUCTS USING ACETIC ANHYDRIDE AS CATALYST Jisheng LIU, Xiaoquan CHEN, Da XUE, Xi LIU, Jianwei XUE,* Fuxiang LI and Zhiping LV College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan 030024, People’s Republic of China Received Septembrie 21, 2017 cyclic utilization The mechanism of chlorination process was investigated by means of experiments and theoretical O Cl O O calculation in this paper. Acetic acid was chlorinated to Cl Cl O OH H3C C H2C C H C C H C C H C C OH 2 2 3 Cl monochloroacetic acid in a laboratory scale glass tube OH Cl Cl + reactor at 105°C. This synthesis reaction was an Cl H (H2SO4, FeCl3) CH3COOH 2 autocatalytic process, acetic anhydride was the catalyst O and the concentrated H2SO4 or FeCl3 was used as H3C C OH promoter. The activation energy of monochloroacetic 2Cl acid, dichloroacetic acid and trichloroacetic acid was Cl O O calculated by the DFT method. The results showed that Cl Cl Cl O Cl OH Cl O H C C CH the generation of monochloroacetic acid via ionic 2 C CH C HC C H2C C OH Cl chlorination mechanism, the generation of by products Cl OH Cl Cl Cl Cl H+(H SO , FeCl ) dichloroacetic acid and trichloroacetic acid mainly via CH3COOH 2 2 4 3 ionic consecutive reaction path which belonged to ionic O H3C C consecutive chlorination mechanism. Moreover, the rate OH controlling step of monochloroacetic acid generation 3Cl was the acetyl chloride acid catalysis enolization, which O formed 1-chloro, 1-ethene-1-olvia acetyl chloride Cl O Cl Cl Cl O Cl O Cl O Cl C C CH C Cl C C C C CH C OH Cl Cl Cl OH Cl Cl Cl Cl Cl Cl + CH3COOH 2 H (H2SO4, FeCl3) INTRODUCTION* literatures. J. Heroid2 found that the reaction proceeds of acetic acid chlorination mainly via a Monochloroacetic acid is a kind of important radical mechanism in the absence of a catalyst, and organic chemical, which has been applied in the dichloroacetic acid was formed consecutively medicine, dyes, perfumes and chemicals of from monochloroacetic acid. While with the agriculture industry, which plays a significant role presence of catalyst, the mechanism was changed, in the field of chemical industry. Due to the and the monochloroacetic acid formation was existence of the chlorine atom in the enhanced, but the dichloroacetic acid formation monochloroacetic acid molecular structure, the was prohibited. P. Martikainen et al3 had studied acidic density and reactivity of monochloroacetic the kinetics of chlorination of acetic acid with acid is stronger than that of acetic acid.1 molecular chlorine with the presence of acetyl The investigation of the mechanism of chloride as a catalyst. G. Sioli et al4 found that the chlorination reactions has been reported in some reaction of acetic acid chlorination was preceded * Corresponding author: [email protected] 236 Jisheng Liu et al. by the following mechanism: the intermediate condenser equipped with low temperature cooling circulating acetyl chloride was enolized firstly, and then added pump was placed on the top of the reactor. The gaseous with chlorine to produce the chloroacetyl, which compounds passed through water, sodium bicarbonate solution and concentrated sodium hydroxide solution before being did rapid chlorine exchange reaction with acetic released to the air. acid to generate the monochloroacetic acid and The acetic acid to be chlorinated was placed in the acetyl chloride. reaction vessel. The slightly excess chlorine feed was Y. Ogata and T. Sugimoto et al5 investigated the introduced, and the liquid phase was heated to the desired ionic mechanism of the sythesis of monochloroace- reaction temperature. A certain amount of acetic anhydride tic acid. Y. Ogata and T. Harada et al6 indicated that was added. Samples of the liquid phase were analyzed by gas chromatograph after esterification.11 di-and trichloroacetic acids were generated by ionic chlorination in the sythesis process of Calculation Methods monochloroacetic acid. Y. Ogata et al6 also found that the chloroacetyl chloride could be produced by Density functional theory method quantum chemistry calculation was adopted and the calculations were performed enolization of acetic acid by acid catalysis added 3 7 by using the Dmol program mounted on Materials Studio with chlorine. T. Salmi et al proposed that the rate- 5.5 package. All the reactions and products in the chlorination determining step of the chorination of acetic acid reaction were optimized and their stable structures were was the acid-catalyzed enolization of acetyl obtained at the same time. All transition states of the reactions chloride. P. Maki-Arvela and T. Salmi8 found that were trialed and searched carefully by using an LST/QST acetyl chloride could be formed in situ in the method, thus, the primitive activation energy and the heat of chlorination process by allowing acetic anhydride reaction were obtained. The nonlocal exchange and correlation energies were calculated with the PW91 function of the to react with HCl, and they proposed the acid- 11 9 generalized gradient approximation (GGA) and a double catalyzed autocatalysis effect. X. Y. Zhou also numerical plus polarization (DNP) basis set in the level of all believed that chlorination of monochloroacetic and electrons. The convergence criteria included threshold values dichloroacetic acids was the ionic mechanism, and of 1 × 10-5 Hartree, 0.02 Hartree per nm, and 0.0005 nm for belonged to the consecutive reactions. P. Maki- energy, force and displacement convergence, respectively, the Arvel et al10 indicated that the generation of self-consistent-filled (SCF) density convergence threshold value was specified as 1×10-6Hartree. A Fermi smearing of dichloroacetic acid had two routes: the ionic 0.005 Hartree was employed to improve the computational mechanisms and the radical mechanisms. performance, and the solvent effect was also considered In order to verify the synthesis mechanism of during the calculations. The geometries of all stationary points monochloroacetic, di-and trichloroacetic acids, the were optimized at this level. Dmol3 program of Materials Studio 5.5 was applied to simulate the mechanism of chlorination of acetic acid using the density function method. RESULTS AND DISCUSSION The results could contribute to promote the production of monochloroacetic acid. The experimental results The effect of different catalyst amounts of EXPERIMENTAL AND CALCULATION acetic anhydride in chlorination: First, the effect of acetic acid catalytic chlorine was investigated (see Experimental Table 1 and Figure l) in the condition of 105°C The chlorination of acetic acid was carried out in a reaction temperature, 40mL/mins chlorine flow homemade glass tube equipped with a magnetic stirring rate and acetic anhydride were 8%; 15%; 20% and apparatus. The glass tube was heated by an oil bath heater with 25% of the quality of acetic acid. a temperature controller. The chlorine gas was metered by a rotameter to disperse into the reaction mixture. A reflux Table 1 The catalyst amount of acetic anhydride in chlorination Acetic Reaction CA MCA DCA anhydride (%) time (h) (%) (%) (%) 8 6 73.37 23.51 3.12 15 6 51.72 45.04 3.24 20 6 21.29 76.41 2.30 25 6 9.53 88.39 2.08 Acetic anhydride as catalyst 237 100 8wt% 80 15wt% 20wt% 25wt% 60 40 20 Monochloroacetic acid wt% acid Monochloroacetic 0 02468 reaction time (h) Fig. 1 – The effect of catalyst amount of acetic anhydride on monochloroacetic acid generation. As shown in Figure 1, the production amount of As was shown in Figure 2 and Table 2. The monochloroacetic acid increased with time after generation rate of monochloroacetic acid was very the addition of acetic anhydride. The generation fast in the first 50 mins with the addition of rate of monochloroacetic acid was slow in the first concentrated H2SO4 or FeCl3, and the yield of 1h and increased remarkably until 6h, then, its monochloracetic acid was 30% and 20% generation rate increased steadily from 6h to 8h. At respectively, however, the yield of monochloroace- the same time, the rate and productions of tic acid was only 4% in the blank experiment. monochloroacetic acid also increased rapidly with Then, the generation of monochloroacetic acid the increase of acetic anhydride mass fraction. increased rapidly from 50 mins to 150 mins, the yield was 97.6% and 91.7%, respectively. And the Moreover, we found that the productions of yield of monochloroacetic acid was 29.5% in the dichloroacetic acid decrease with the increasing of blank experiment. Moreover, the yield of acetic anhydride mass in Table 1. monochloroacetic acid began to decrease to 94.2% The influence of concentrated H2SO4 and FeCl3 with the increase of concentrated H2SO4 catalyst catalyst promoter in chlorination: In order to verify promoter, but the yield of monochloroacetic acid the catalytic principle, 1.5% FeCl3 and 5% kept on increase with FeCl3 catalyst promoter and concentrated H2SO4 were added in the experiment reached 95.8% during 150 mins to 200 mins. Then, of acetic anhydride catalytic chlorination. The when the reaction time reached 150mins, the yield comparison of the chlorination reaction and the of dichloroacetic acid was 0.74%, the yield of blank experiment indicated the catalytic effect of dichloroacetic acid was 2.01% and 2.79% with the acid and autocatalytic of the reaction. Chloride concentrated H2SO4 and FeCl3 catalyst promoter, products were analyzed by gas chromatography respectively, which was higher than the yield of (see Figure 2 and Table 2). dichloroacetic acid in the blank experiment. Table 2 The influence of catalyst promoter on monochloroacetic acid Reaction Catalyst Mass CA MCA DCA time promoter (%) (%) (%) (%) (min) blank 0 150 69.9 29.5 0.74 H2SO4 5 150 0.44 97.6 2.01 FeCl3 1.5 150 0.09 91.7 2.79 238 Jisheng Liu et al.