Ind. Eng. Chem. Res. 1992, 31, 431-434
431
New Approach for the Simple and Economic Preparation of Inorganic Bromide Salts Ronit Aizenberg, Onn Arrad, and Yoel Sasson* Casali Institute of Applied Chemistry, School of Applied Science and Technology, The Hebrew University of Jerusalem, 91904 Jerusalem, Israel
A variety of inorganic bromide salts are prepared from the respective chloride salts by reaction with 1,2-dibromoethane. The reaction is carried out under convenient phase-transfer catalytic conditions. The conversion and yield are quantitative; the reaction equilibrium is shifted by in situ distillation of the organic product, 1-bromo-2-chloroethane. The proposed technique is suited for large-scale production of common inorganic bromides as well as for the laboratory-scale preparation of commercially unavailable bromide salts.
Introduction Inorganic bromide salts are generally prepared by neutralization of the respective base with hydrobromic acid (Kirk-Othmer, 1978; Ullmann, 1985). This method has several drawbacks, such as the higher price of hydrobromic acid compared to bromine, the highly corrosive reaction medium, the need to control the large amount of heat evolved, and the low solubility of some of the bases used. Finally, the bases of some metals are not available commercially. Alternatively, inorganic bromides are manufactured by the reaction of a basic metal compound with elemental bromine, which requires a stoichiometric amount of a reducing agent; again the reaction medium is extremely corrosive. Other procedures, such as the direct attack of hydrobromic acid on the pure metal, have similar drawbacks and are not used commercially. The halogen-exchange reaction has been thoroughly investigated as a tool for the synthesis of organic halides (Finkelstein, 1910; Dillon, 1932; Henne and Mildley, 1936; Teuscher, 1950; Bailey and Fujiwara, 1955; Landini et al., 1974a,b; Liotta and Harris, 1974; Cinquini et al., 1975; Willy et al., 1976; Tundo, 1979; Dermeik and Sasson, 1983). The bromide-chloride exchange between inorganic salts and primary alkyl halides is a two-phase equilibrium reaction (eq 1). It can be carried out conveniently by the application of phase-transfer catalysis (Starks and Liotta, 1978); a solvent is not required (Yonovich-Weiss and Sasson, 1984, 1985; Sasson et al., 1986). K
MCl(aq) + RBr(org) e MBr(aq) + RCl(org) (1) To our knowledge, the usefulness of the halogen-exchange reaction for the preparation of inorganic compounds has not been realized yet. The present paper deals with the quantitative conversion of various inorganic chloride salts to the respective bromides. For this purpose the low-priced commodity 1,2-&bromoethane (DBE) seems to be the organic bromide source of choice. In the past, DBE has been used mainly as an additive to leaded fuels. Due to the continuing switch to unleaded fuels in recent years, the supply of this chemical exceeds demand. Another advantage of the use of DBE as a bromide source is the increased safety and the cost reduction in the handling and transportation of this substance in comparison with the highly corrosive bromine or hydrobromic acid. Among the various inorganic bromides, we have focused our research on the preparation of calcium bromide. This compound has drawn our attention because of the increasing use of its aqueous solutions (50%) in oil explorations, as a substitute for the common drilling muds (Bassett et al., 1988; Kirk-Other, 1978). The respective inorganic starting material, aqueous calcium chloride, is
a waste product of various chemical processes, and its economic value is negative.
Results and Discussion We have investigated the influence of some key variables on the equilibrium composition and the kinetics of the reactions. The reactions were carried out by mixing aqueous solutions of calcium chloride with 1,Bdibromoethane (DBE) without solvent a t 90 "C, in the presence of 2% didecyldimethylammonium bromide (DDAB) as a phase-transfer catalyst (eqs 2 and 3). The conversion of f/2CaClz(aq)+ QBr(org) += f/&aBrz(aq) + QCl(org) (2) QCl(org) + RBr(org) QBr(org) + RCl(org) (3) Q = quaternary ammonium cation calcium chloride was followed by potentiometric titration; the organic phase composition was counterchecked by gas chromatography (GC). The reactions were stopped after 48 h. Thermodynamic equilibria were obtained; appropriate reverse reactions which we have carried out gave the same compositions. With a DBE/calcium chloride reagent ratio of 3:1, the equilibrium conversion of calcium chloride is 8490,as long as the initial salt concentration of the aqueous phase is up to 30 wt %; above this concentration the conversion is strongly reduced (Figure 1). It should be noted, that full conversion of a 30% solution of calcium chloride yields a 50% solution of calcium bromide, due to the higher molecular weight of the later. The equilibrium conversion of calcium chloride can be raised to 95%, by increasing the reagent ratio from 3 to 10 (Figure 2). Addition of an organic solvent slightly reduces the conversion (Figure 3); the temperature (60-110 "C) has a negligible influence. The strong influence of the aqueous-phase composition has been explained before (Yonovich-Weiss and Sasson, 1985; Sasson et al., 1986). It results from the preferred hydration of calcium bromide in comparison with calcium chloride in concentrated solutions (the activity coefficient rBrbecomes greater than ~ ~ l -This ) . preferred hydration changes the selectivity of the extraction by the quaternary ammonium cation (eq 2) in favor of the bromide anions; i.e. the ratio of Q+Br-(org)/Q+Cl-(org)increases, and both the chemical reaction equilibrium (eq 3) and the overall equilibrium (eqs 1 and 4) are shifted to the left. [RBr(org)1rcr[C1-(aq) 1 = ([RCl(org)1rBr-[Br-(ad 1) /K (4)
Various quaternary ammonium salts were tested as catalysts for this transformation. As expected the equilibrium composition is not effected, but a strong influence on the reaction kinetics was found. All the reactions follow reversible pseudo-first-order kinetics, up to at least 70%
0888-588519212631-0431$03.00/0 0 1992 American Chemical Society
432 Ind. Eng. Chem. Res., Vol. 31, No. 1, 1992 3.0
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M A B -Tetraoctylammonium bromide THAB -Tetrahexylammonium bromide DDAB -Didecyldimethylammonium bromide Aliquat 336 -Trioctylmethylammonium chloride TBAB -Tetrabutylammonium bromide
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Figure 1. Effect of the aqueous salt concentration on the equilibrium conversion of calcium chloride. RBaction conditions: DBE, 0.09 mol; aqueous CaCl,, 0.03 mol; DDAB, 6 X lo4 mol; 90 O C ; 48 h.
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Figure 4. Effect of the catalyst type on the reaction rate, k, reversible fvetorder rate constant (min-l X 109). Reaction conditions: DBE, 0.09 mol; 30% aqueous CaC1, (0.03 mol); catalyst,6 X 1a-l mol; 90 OC. The number of C atoms of the various catalysts is noted on the bars.
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Figure 2. Effect of initial 1,2-dibromornethane/calciumchloride ratio on the equilibrium conversion of calcium chloride. Reaction conditions: 30% aqueous CaC1, (0.03 mol); DDAB, 6 X lo4 mol; 90 OC; 48 h.
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Figure 3. Effect of solvent on the equilibrium conversion of calcium chloride. Reaction conditions: DBE, 0.09 mol; 30% aqueous CaCl, (0.03 mol); DDAB, 6 X l p mol; solvent, 25 mL; 90 OC; 48 h.
of equilibrium conversion, but only catalysts with more than 20 carbon atoms give acceptable reaction rates ( F i e 4). The rate increased linearly with the catalyst concentration, at least up to a catalyst/DBE ratio of 0.1. The pseudo-first-order kinetics observed are a result of a chemical reaction (eq 3) controlled rate, with a steadystate concentration of Q+Cl-(org),which is maintained by the rapid ion exchange process (eq 2). The concentration of the aqueous phase has a relatively strong influence on the reaction kinetics too; the higher
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Innlal calcium chlorld. conuntratlon (weight W )
Figure 5. Effect of the aqueous salt concentration on the reaction rate, k, reversible first-order rate constant (min-' X 109). Reaction conditions: DBE, 0.09 mol; 30% aqueous CaClz (0.03 mol); DDAB, 6 X lo-' mol; 90 OC.
the salt concentration,the lower the reaction rate (Figure 5 ) . As in the shift of the equilibrium composition, the effect is due to the decreasing Q+Cl-(org) steady-state concentration. It should be mentioned that dehydration of the organic ion pair would be expected to increase the reaction rate (Landini et al., 1978), but due to the small dessicating properties of even concentrated calcium halide solutions, we have not observed such an effect with increasing salt concentration of the aqueous phase (Landini et al., 1982).
Synthetic Application The phase-tranefer catalyzed reaction between DBE and inorganic chlorides can be conveniently utilized for the quantitative preparation of inorganic bromides, provided that the equilibrium is drawn to the right. Since the reactions are carried out in the absence of an organic solvent, this shift can be achieved by fractional distillation of the 1-bromo-2-chloroethane (BCE) formed during the reaction; the water codistilledduring the reaction is returned to the reaction vessel. We have applied this technique successfully for the preparation of various bromides; the purity and yield of the products are generally above 98% (Table I). At the end of the reactions, which are completed w i t h 8-10 h, the inorganic product is isolated quantitatively;
Ind. Eng. Chem. Res., Vol. 31, No. 1, 1992 433 Table I. PreDaration of Inorganic Bromide Salts salt prepared product yield and purity/ % Carz 97.8 NaBr 98.9 KBr >99 LiBr CuBrz NiBrz Barz CrBrB
>99 >99
98.4 >99 >99
after phase separation the 50% aqueous solution can be marketed as such, or the solid product can be obtained by evaporation of the water. The quaternary ammonium catalyst remains completely dissolved in the organic phase and can be recycled. Some remarks should be made concerning the distillation. In the preaence of aqueous solutions, DBE, BCE, and DCE (1,2-dichloroethane)boil at their azeotropic boiling points (95, 84, and 72.5 "C, respectively) rather than at their boiling points as pure compounds (131.3, 107, and 83.5 "C, respectively). This boiling point alteration causes two problems: Firstly, it limits the reflux temperature of the reaction mixture, which in turn is responsible for the relatively long reaction duration. Secondly, it reduces the efficiency of the distillative separation of the organic compounds. The high conversion (298%)of the inorganic chloride can be achieved only if the alkyl chloride content of the organic phase in the reaction vessel, in the final stage of the reaction, is kept at 2% or less. As a result, the organic distillate obtained toward the end of the reaction (at least in our laboratory procedure) contains more than 80% of dibromoethane. The 1,2-dibromoethane lost can be easily recovered from the organic distillate, by a second distillation in the absence of an aqueous phase. Under these conditions, the separation of the two organic components does not cause any difficulties. When l-bromo-2-chloroethaneis not removed during the reaction, it accumulates in the organic phase, until 1,2dichloroethane begins to form. Selective distillation of that compound shifts the composition of the organic solution, and theoretically it could be made in this way the sole organic product of the process. Practically this cannot be achieved, due to the limit of 2% alkyl chloride content in the reaction mixture (which includes of course l-bromo2-chloroethane), toward the end of the reaction. So whenever the organic product required is dichloroethane, it has to be separated from the l-bromo-2-chloroethane, which is codistilled in the final stages of the reaction. Since eq 3 is valid for different types of primary alkyl groups (Sasson and Yonovich-Weiss, 1981), 19-dibrornoethane can be also used as an organic bromide source for the preparation of primary alkyl bromides from the respective chlorides (eq 5 ) . The alkyl chloride must have
Q+X-,
RCl(org) + R'Br(org1 RBr(org) + R'Cl(org) (5) a boiling point of 125 "C, at least, so that the formed 1-bromo-2-chloroethane can be removed selectively by distillation. We have demonstrated the usefulness of the reaction in the preparation of 1-bromooctane and benzyl bromide with quantitative conversion of the respective chlorides. No aqueous phase is present in this type of reaction. As a result, hydration of the quaternary ammonium salt is rather low, and the reflux temperature of the reaction mixture increases to 135 "C at atmospheric pressure. To avoid catalyst decomposition, we have carried out these reactions under reduced pressure (300-400 Torr), so that the reaction temperature was about 100-110 "C. This is still far above the temperature of the two-phase
reactions, and the reactions were completed within 1 or 2 h, due to the increased reaction rates. The absence of an aqueous phase has another advantage: it increases the efficiency of the distillative separation. To summarize,in this article we have described a simple technique for the preparation of inorganic (or organic) bromides which avoids the corrosive and exothermic conditions of the conventional processes; the application of 1,Zdibromoethane as the bromide source offers some economic advantage. The technique can be scaled up to a process for the manufacture of the respective bromide compounds, without difficulty. Concerning specialty bromide compounds, a batch process might be appropriate, but production on a larger scale would be best carried out in a continuous flow stirred tank reactor. In both cases 1-bromo-2-chloroethanehas to be removed by distillation during the reaction. The reduced effectiveness of the distillation column, caused by the codistilling water, requires either the construction of a highly efficient column with a large number of plates or the performance of a second distillition, after the phase separation, for the final isolation of BCE. Our results indicate that the second possibility is more appropriate.
Experimental Section Materials. Chemically pure or technical reagents can be used according to the required specifications. Analytical Procedure. The composition of the reaction mixture was determined by concurrent analysis of both the organic phase and the aqueous phase. The organic phase was analyzed by GC, which was calibrated with pure reference substances. The composition of the aqueous phase was determined by potentiometric titration with 0.1 N AgNO,. The end point was calibrated with chloride/ bromide standard solutions (bromide anion content, 2-98%). Some of the results were confirmed by HPLC analysis on an ion-exchange column. General Reaction Conditions. All the inorganic bromide salts were prepared as described for calcium bromide: 1,2-dibromoethane (1.5 mol, 281.7 g), aqueous calcium chloride (30 wt % ,0.5mol, 55.5 g of CaClJ, and didecyldimethylammonium bromide (0.02 mol, 8.1 g) were placed in a three-necked round-bottom flask, equipped with a mechanical stirrer and an isolated distillation column (1 m), filled with small glass fragments, on top of which a Dean-Starks apparatus for azeotropic distillation was mounted. The reaction mixture was heated to reflux; the heating rate was adjusted to allow for the distillation of l-bromo-2-chloroethane,which was formed by the reaction. This procedure was continued until a calcium chloride conversion of 98% was reached. At this point the reaction was stopped (10 h). Product Isolation. The inorganic salt was obtained quantitatively (98 g) after phase separation, water evaporation and drying; it had a calcium bromide content of 97.8%. The organic phase from the reaction vessel (43 g) contained about 98% DBE, 2% BCE, and the catalyst and could be recycled with an appropriate makeup of DBE. The organic product, 1-bromo-2-chloroethane(0.87 mol, 124.7 g) was isolated from the organic distillate by a second distillation stage; a first small fraction collected contained mainly 1,2-dichloroethane (less than 0.02 mol). The residue from this distillation (60.6 g) contained a mixture of DBE (-90%) and BCE. Registry No. TBAB, 1643-19-2;DMF, 68-12-2;TOAB, 14866-33-2;THAB, 4328-13-6; DDAB, 2390-68-3;Br(CH&Br, 106-93-4;Br(CH&Cl, 107-04-0;CaBrP,7789-41-5; NaBr, 7647-15-6; KBr, 7758-02-3;LiBr, 7550-36-8;CuBrz, 7789-45-9;NiBrz, 13462-88-9;BaBrz, 10563-31-8;CrBra, 10031-25-1;(M&C6H4,
I n d . Eng. Chem. Res. 1992,31,434-439
434
1330-20-7; C P h , 108-90-7; H(CH2I6OH,111-27-3; CaCl,, 1004352-4; NaC1, 7647-14-5; KCl, 7447-40-7; LiC1, 7447-41-8; CuC12, 7447-39-4; NiC12,771854-9; BaC12, 10361-37-2; CrC13, 10025-73-7.
Landini, D.; Maia, A; Podda, G. Nonhydratd Anion Transfer from the Aqueous to the Organic Phase: Enhancement of Nucleophilic Reactivity in Phase-Transfer catalysis. J . Org. Chem. 1982,47,
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Bailey, W. J.; Fujiwara, E. Mixed Dihalides and Halohydrins from Butynediol. J . Am. Chem. SOC.1955, 77, 165. Bassett, D.; Chetland, J.; Kyte, A. B.; Marsden, H. M.; Roberts, P. N.; Summer, W. N.; Watkins, D. Introductory Review. In Bromine Compounds, Chemistry and Applicatiom; Price, D., Iddon, B., Wakefield, J., Eds.; Elsevier: Amsterdam, 1988; Chapter 1, p 106.
Cinquini, M.; Montanari, F.; Tundo, P. Alkyl Substituted h a macrobicyclic Polyethers: Highly Efficient Catalysts in Twophase Reactions. J . Chem. SOC.,Chem. Commun. 1975,393. Dermeik, S.; Sasson, Y. Preparation of Primary Alkyl Fluorides by Phase Transfer Catalysis. J. Fluorine Chem. 1983,22,431. Dillon, R. T. The Reaction Rate of Potassium Iodide with Dibromides of the Ethylene Bromide Type. J. Am. Chem. SOC. 1932, 54, 952.
Finkelstein, H. Darstellung organischer Jodide aus den entsprechenden Bromiden und Chloriden. Ber. Dtsch. Chem. Ges. 1910, 43, 1528.
Henne, A. L.; Mildley, T. Mercuric Fluoride, a New Fluorinating Agent. J . Am. Chem. SOC.1936,58,884. Kirk-Othmer's Encyclopedia of Chemical Technology, 3rd ed.; Wiley: New York, 1978; Vol. 4, pp 244-5. Landini, D.; Montanari, F.; Pirisi, F. M. Crown Ethers as Phasetransfer Catalysts in Two-phase Reactions. J. Chem. SOC.,Chem. Commun. 1974a, 879. Landini, D.; Montanari, F.; Rolla, F. Reaction of Alkyl Halides and Methanesulphonates with Aqueous Potassium Fluoride in the Presence of Phase Transfer Catalysts: a Facile Synthesis of Primary and Secondary Alkyl Fluorides. Synthesis 197413,428. Landini, D.; Maia, A.; Montanari, F. Phase-Transfer Catalysis. Nucleophilicity of Anions in Aqueous Organic Two-Phase Reactions Catalyzed by Onium Salts. A comparison with Homogeneous Organic Systems. J . Am. Chem. SOC.1978,100, 2796.
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Sasson, Y.; Yonovich-Weiss,M. Halogen Exchange Reactions Catalyzed by Amines. J . Mol. Catal. 1981,10, 357. Sasson, Y.; Weiss, M.; Loupy, A.; Bram, G.; Pardo, C. BromideChloride Exchange Between Alkyl Halides and Metal Halide Salts Under Solid-Liquid Transfer Conditions Without Added Organic Solvents. J. Chem. SOC.,Chem. Commun. 1986, 1250. Starks, C. M.; Liotta, C. L. Phase Transfer Catalysis. Academic: New York, 1978; pp 117-22. Teuscher, P. Solvolysis and Rearrangement Reactions Accompanying the Formation of Methallyl Bromide. J. Am. Chem. SOC.1950, 72, 4316.
Tundo, P. Nucleophilic Substitution Between Gaseous Alkyl Halide and a Solid Salt, Promoted by Phase-Transfer Catalysis. J. Org. Chem. 1979,44, 2048. Ullmun's Encyclopedia of Industrial Chemistry, 5th ed.; VCH Verlagsgesellschaft Weinheim, Germany, 1985; Vol. A4, pp 423-4.
Willy, W. E.; McKean, R.; Garcia, B. A. Conversion of Alkyl Chlorides to Bromides, Selective Reactions of Mixed Bromochloroalkanes, and Halogen Exchange. Bull. Chem. SOC.Jpn. 1976,49, 1989.
Yonovich-Weiss, M.; Sasson, Y. Synthesis of Primary Alkyl Bromides by Halogen Exchange with Calcium Bromide under Phase Transfer Conditions. Synthesis 1984, 34. Yonovich-Weiss, M.; Sasson, Y. Phase Transfer Catalyzed Bromide-Chloride Exchange: Dependance of Equilibrium Position and the Selectivity Constants on Nature and Composition of the Aqueous Phase. Zsr. J. Chem. 1985,26, 243. Received for review May 20, 1991 Accepted August 20,1991
Corrosion Inhibition of Structural Steels in C 0 2 Absorption Process by Organic Inhibitor Composed of 8-Aminothiophenol, ( 1-Hydroxyethylidene)bis(phosphonic acid), and Diethanolaminet Isao Sekine,* Tetsuya Shimode, and Makoto Yuasa* Department of Industrial Chemistry, Faculty of Science and Technology, Science University of Tokyo, 2641 Yamazaki, Noda, Chiba 278, Japan
Koichi Takaoka Keiyo Plant Engineering Co., Ltd., 2-8-8 Zchikawa-minumi, Zchikawa, Chiba 272, Japan
Corrosion inhibition of mild steel (JISSS 41, UNS K02600) and stainless steel (type 304, UNS S30400) in hot K2CO3 solution containing 2-aminothiophenol (ATP) was investigated by physicochemical measurements. Inhibition for formation of FeCO, as scale was also investigated. The maximum value of inhibition efficiency (9) of corrosion for SS 41 in 50 ppm ATP solution under atmospheric conditions was ca.90% and was close to those obtained in solutions containing passivators of Na&kO, and V20,. In the mixed solutions of (a) ATP and (1-hydroxyethylidene)bis(phosphonic acid) (HEDP) and (b) ATP, HEDP, and diethanolamine (DEA), they exerted a cooperative effect of inhibition of SS 41. In a bench-scale test using the Benfield apparatus, the r] value of type 304 in the solution containing ATP under high pressure and temperature was ca. 95% and was similar to those obtained in solutions containing passivators. In solutions containing (a) ATP and HEDP and (b) ATP, HEDP, and DEA, HEDP inhibited the formation of FeC0, as scale. Introduction Hot, aqueous solution of potassium carbonate (K2C03) has been widely used in the process of removing carbon After absorbing C 0 2this solution leads to dioxide ((20,). 'This paper is second in a series on corrosion inhibition of structural steels in the C 0 2 absorption process by organic inhibitors. oaaa-5aa51921263 1-0434$03.00/
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a high corrosive property (Banks, 1967; Bienstock and Field, 1961) and is sensitive to stress corrosion cracking (SCC) (Forouris,1987; Johnson, 1987; Naito et al., 1978). Some inorganic compounds.suchas potassium bichromate (K2Cr20,), vanadium oxide (V,O,), and substrate with nickel (Ni) ion had been developed as corrosion inhibitors in the C 0 2 absorption process (Field and Bienstock, 1965; Gancy and Durling, 1978; Eickmeyer, 1969). However, 0 1992 American Chemical Society
