PRODUCT REVIEW
Bromine Chloride: an Allternative to Jack F. Mills* and John A. Schneider The Dow Chemical Company, Midland, Mich. 4864.0
DR. JACK F. MILLS received his B.A. Degree from Knox College and his Ph.D. Degree in Organic Chemistry from the State University of Iowa. I"ol1owinq a year of p o s t doctorate work at the University of Illinois he spent two years as the Industrial Research Liaison for the Army Chemical Corps Research and Development Command. Dr. Mills joined The Dow Chemical Company in 1956 and i s presently a Research Specialist in the Halogens Research Laboratory. Dr. Mills' experience with Daw includes his work with the development and applications of organic and inorganic halogen compounds. H E i s author and coauthor of ten publications and several patents dealing with halogen compounds. He i s presently past chairman of the Midland sectwn of the American Chemical Society.
I
DR. JOHN A. SCHNEIDER received an A.B. Degree from Albion College and his Ph.D. Degree in Organic Chemistry from the Massachusetts Institute of Technology in 1966. From. 1964 through 1966, Dr. Schneider taught chemistry at Cambridge Junior College, Cambridge, Mass. He joined Dow in 1966 and i s presently a Research Specialist in Ag-Organics R&D. Dr. Schneider has been involved in antibwtic synthesis, peptide methodology, halogen chemistry, $re retardancy, coatings, styene-butadiene latexes, and amines with publications on cepham synthesis, s y w thetic peptide catalysis, tetrajluoroborate chemistry, polyester synthesis, bromine, and $re retardancy.
160 Ind. Eng. Chem. Prod.
Rei. Develop., Vol. I?, No.
3, 1973
T h e increased attention being paid t o waste problems and process improvements indicates, among other things, a need for more and better process alternatives. The use of bromine chloride as a brominating agent offers a n alternative process with important cost and ecological advantages. Since BrCl contains more active bromine and reacts more readily than elemental hromine, greater product yields and less by-products are often obtained. A major advantage is t h a t the main byproduct of bromine chloride substitution reactions is HC1. Although chemists have long been familiar with many of the properties of bromine chloride, the compound has been little used in industrial processes until very recently. This neglect has occurred even though bromine chloride appears t o have many advantages, some of which follow. Bromine chloride reacts much more rapidly t h a n bromine. (Burger, et al., 1960; Schnlek and Burger, 1958a, 1960). With aromatic compounds, the reaction rate is on the average about 100 times that of bromine, while with some olefinic compounds, a 200-fold increase in reaction is obtained (White and Robertson, 1939). Bromine chloride has much greater oxidizing power than bromine, as shown by its faster and more complete oxidation of alcohols (Konishi, et al., 1968). Dry bromine chloride is 1-2 orders of magnitude less corrosive than dry bromine t o such meta.ls as low-carbon steel, stainless steel, nickel, and Monel. Neither moist nor dry bromine chloride shows any evidence of causing stress corrosion cracking of stainless steel (Mills and Oakes, 1973). Bromine chloride has a much lower freezing point (-65') than bromine (-7.0°), so that heated or insulated storage is not required during winter months. Bromine chloride contains 69.3% reactive bromine*% more available bromine than molecular bromine contributes t o substitution reactions. Thus, 0.72 lb of bromine chloride is equivalent t o 1.0 Ib of bromine. Despite these pronounced advantages, industrial processors and other users have displayed reluctance to use BrCl in the past partly from the lack of handling and process technology. Concern about side reactions such as chlorination may also have been a factor, since BrCl exists in an equilibrium mixture containing molecular chlorine and bromine. However, recent studies using liquid BrCl have made such problems no longer a major concern.
Bromine chloride offers to manufacturers of bromine products an alternative brominating agent with higher chemical reactivity, no costly waste bromide liquors, and lower bromine corrosivity.
General Properties of Bromine Chloride
Liquid BrCl is best stored in cylinders or vessels containing a dip pipe whereby t h e liquid may be removed under its own pressure (30 psig, 25"). Thus, precise and predictably uniform quantities of liquid BrCl can be routinely withdrawn from storage vessels provided t h e material is removed as a liquid rather than a vapor. Likewise, although bromine chloride is about 40% dissociated into bromine and chlorine in most solvents, its high reactivity and fast equilibrium often produce bromine products resulting almost exclusively from BrCl. This is illustrated by Scheme I showing the major types of Scheme I. Typical Reactions of Bromine Chloride Br
H20
HCI t HOBr
\ BrCl / -RBr
RH
HCI t N H 2 B r
t HCI
c-c Br CI
reactions t h a t bromine chloride can undergo. The diagram reveals t h a t in almost all cases t h e product formed contains bromine. With the exception of reactions involving t h e addition of bromine chloride t o olefins, hydrogen chloride is produced as a by-product, whereas similar uses of elemental bromine result in by-product hydrogen bromide. The latter not only represents a waste of bromine, but its disposition may have a significant impact on plant design and cost. Uses for Bromine Chloride
Although t h e primary use for bromine chloride is as a brominating agent, its potential lower cost and advantageous properties suggest other uses similar to those of chlorine such as disinfection, oxidation, and bleaching. Specific uses as a brominating agent may include production of bromine containing fire retardants, agricultural chemicals, pharmaceuticals, organic dyes, high-density fluids, and various chemical intermediates. Several process studies have been made of bromine chloride use in these areas by The Dow Chemical Co. Also a number of reports have shown utility of bromine chloride as a n analytical reagent (Schulek and Burger, 1958a, 1959, 1960). Most of these uses take advantage of t h e high reactivity and selectivity of BrCl reactions with various compounds. Physical Properties of Bromine Chloride
As a n equilibrium mixture, bromine chloride is a fuming dark red liquid below 5". Pure bromine chloride exists only a t relatively low temperatures in the solid state (Emeleus and Anderson, 1960). Therefore, precise determinations of t h e physical properties of bromine chloride are prevented by its dissociation. Thus, values given for t h e melting point and boiling point of bromine chloride are in reality equilibrium temperatures for t h e phase changes. Although the vapor pressure of dissociated liquid bromine chloride reaches 760 mm a t So,a temperature of 36" is required before the vapor above
Table I. Physical Properties of Bromine Chloride Compared to Bromine.
?If01 W t yo bromine Fp, "C Bp, "C, 760 mm 226 mm 100 mm 10 mm 5 atm 10 a t m Density, g/cm3, 15' 20" 25" 30' lb/gal, 25" Vapor density, gjl., std condit'ions (0",1 atm) Latent heat of fusion, cal/g Latent heat of vaporizn, cal/g, b p 25" Heat capacity, caljdeg mol, 298°K Entropy, cal/deg mol, 298°K Dipole moment, D Kormal redox potential, V a Mellor (1956).
BrCl
Brz
115.37 69.27 -66 5 - 30 - 56 ... 70 2.352 2.339 2.324 2.310 19.3 5,153
159.83 100 -7.27 58.8 25 6 - 32 ... 139.8 3.1396 3.1226 3.1055 3.0879 25.8 7.139
17.6 53.2 30.0 8.38 57.34 0.56 1.30
15.8 44.9 46.2 18.09 36.35 0 1.09
48
the liquid attains the same composit'ion as the liquid (Greenwood, 1956). As mentioned before, a n important advantage of its freezing point (-65') being lower than t h a t of bromine (-7") is that heated and insulated storage is not required during the winter months. Table I compares a number of the reported physical properties of bromine chloride with those of bromine. The vapor pressure-temperature curve for bromine chloride is compared t o the separate curves for bromine and chlorine in Figure 1. The vapor pressure curve for a 30y0 solution of bromine chloride in methylene chloride is also shown to indicat,e the effect of a typical bromination solvent. The gauge pressure of vessels containing liquid bromine chloride is 30 psig a t 25' which is sufficient pressure to remove t h e liquid t'hrough a cylinder dip tube a t ordinary temperatures. Due to its polarity, BrCl shows greater solubility than bromine in polar solvents. I n water, BrCl has a solubility of 8.5 g/100 g, a t 20°, which is 2.5 times the solubility of bromine. I t s solubility in water is increased markedly by adding chloride ion to form t h e complex chlorobromate ion, BrCIz-. -kt lower temperatures bromine chloride forms a yellow, crystalline hydrate, BrC1.7.34Hz0, mp 18" (1 a t m ) (Glew and Hames, 1970). Dissociation of Bromine Chloride
Bromine chloride exists in equilibrium with bromine and chlorine in both t h e gas and the liquid phase (Barratt and Stein, 1929; Vesper and Rollefson, 1934). 2BrCl
Brz
+ Clz
The posit'ion of the equilibrium in the gas phase and in solvents such as carbon tetrachloride has been well established Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 3, 1973
161
lo00
800b
[
1
B i m i n e Chloride
Temperature.
O F
Starting material
60
20
1
2
4
Table II. Reactions of Bromine Chloride w i t h Aromatic Compounds
6 810 20 40 6080100 Absolute Vapor Pressure,psi
200
400
1000
Figure 1. Vapor pressure-temperature curves for bromine, bromine chloride, and chlorine. Vapor pressures were measured by a static method using a Heise Bourdon tube pressure gauge
by spectrophotometric measurements (Popov and hlannion, 1952). There is little information on t h e equilibrium in t h e liquid state, but a recent study using chemical methods indicates significantly less dissociation (less than 20%) in the liquid phase (Alley and Mills, 1972). The rate at which equilibrium is reached among t h e three components of the mixture will vary depending upon the method of formulating bromine chloride. For example, in the gaseous state in the dark, equilibrium was attained in 16-60 hr (Vesper and Rollefson, 1934). I n carbon tetrachloride solution, formation required several seconds (Barratt and Stein, 1929). Bromine chloride in polar solvents requires less time to reach equilibrium than in nonpolar solvents. If the formation of BrCl is relatively slow compared t o the rate of halogenation with bromine or chlorine, unwanted reactions can occur. For example, when BrCl is formed either in situ or just prior t o introduction into a reaction vessel by metering together streams of gaseous bromine and chlorine, there are significant amounts of chlorination and other undesirable side reactions observed. Therefore, it is advantageous to use preformed liquid BrCl and conditions which allow fast equilibration and minimum side reactions. The equilibrium constant for the vapor-phase dissociation of BrCl is close to 0.34, corresponding t o a degree of dissociation of 40.3y0 at 25' (Cole and Elverum, 1952). The dissociation at 500' is 46.4%, showing t h e equilibrium constant varies little with temperature. I n carbon tetrachloride solution, the equilibrium constant was determined spectrophotometrically t o be 0.381 i 0.008, corresponding t o a degree of dissociation of 43.2% a t 25'. Essentially the same results were obtained at 10 and 15' (Popov and Mannion, 1952). Bromine chloride appears t o be more stable in aqueous hydrochloric acid than in a solution of carbon tetrachloride or as a gas. Schulek and Burger (1960) have demonstrated that such a solution of BrCl (probably existing as Br(HCl)G+) can stand for 3 months with very little loss in BrCl content. The equilibrium constant for its dissociation in 4 and 6 X hydrochloric acid is 0.0179, corresponding t o a significantly low dissociation of 3.5% (Forbes and FUOSS, 1927). Reactivity of BrCl Compared to Bromine
As mentioned before, several people have reported t h a t BrCl reacts considerably faster than bromine. This increased reaction speed is probably due t o t h e polarity of the compound, which can be shown as +Br-Cl-. The polarity of bromine chloride is undoubtedly part of the reason t h a t very little chlorination is observed in electrophilic substitution reactions. As a result of its polarity, BrCl will undergo some reactions that do not take place with bromine. When reactions do occur, 162 Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 3, 1973
Yield,
%
Product
Comment
Bromobenzene 9 a PBromoethylbenzene 83 a 2,5Dibrornc-p-xylene 70 a 3-Bromonitrobenzene 43 b Tetrabromobisphenol A C 91 m-Bromobenzoyl chlo81 d ride m-BromobenzenesulBenzenesulfonyl 73 d fonyl chloride chloride p-Bromoanisole ;inisole 83 d 0- and p-bromotoluene Toluene 75 d Bromotrifluorotoluene 90 Trifluorotoluene e Tribromophenol 100 Phenol f 2,&Dibromo-Cnitrop-Nitrophenol 96 9 phenol 2-Hydroxy-5bromcSalicylic acid 100 h benzoic acid 2-Chloro-&bromophenol 0- Chlorophenol 74 i 2-Chloro-Cbromophenol 22 2,6-Dibromophenol o-Bromophenol i 57 2,CDibromophenol 35 PBromo-o-cresol i o-Cresol 61 6-Bromo-0-cresol 28 i PBromo-2-tertbutylo-tert-Butyl50 phenol phenol 6-Bromo-2-tert-butyl35 phenol PBromo-Zphenylo-Phenylphenol i 65 phenol 6-Bromo-2-phenyl22 phenol 4-Bromochlorobenzene 85 Chlorobenzene a Reactions were run neat at 0-30" using iron catalyst. * Reaction run neat at 30" using AlC13 catalyst. Reaction was run in methylene chloride at 0-30°C without a catalyst. Britton and Tree (1952). e McBee, et al. (1950). Burger, et al. (1960). 0 Obenland (1964). * Schulek and Burger (1959). Dietzler and Bradley (1969).
Benzene E thylbenzene p-Xylene Nitrobenzene Bisphenol A Benzoyl chloride
J
yields can often be improved by substituting BrCl for bromine. These facts are illustrated by the examples
2
(CH2)3S~CI
BrCl
"
3
a
-
3 BrCl
No reaction B ~ C H Z S ~ ( C H ~.t) ~HCI C I (Speier, 1951)
a
Low yields (McBee e t at., 1950) CF3
90% yield
'Br
Schulek and Burger (195813) studied the reaction of BrCl n i t h several phenolic compounds and compared the rates t o those obtained with bromine. I n each case, BrCl was a more rapid brominating agent than molecular bromine. More quantitative data u'ere obtained in another study comparing the reaction rates of BrCl to bromine with a variety of aromatic hydrocarbons (LaBarge and Mills, 1973). I n this study, the rapidity ratio, defined as K B ~ c I / K ranged B ~ ~ , from a low of 4.31 for phenetole a t 25' to 286 for p-cresol at 35'. On the average, BrCl proved to react more than 100 times faster than molecular bromine. I n oxidation reactions, BrCl also shows high reactivity. A comparison of oxidation rates of primary and secondary alcohols by aqueous BrCl and bromine was reported by
100
Table 111. Preparation of Hexabromobenzene from Benzenea Temp, Halogen
Catalyst
"C
Time, hr
BrCl FeC1, 40 1.0 Brz FeC13 100 20.0 40 0.25 BrCl AlC13 40 2.0 Brz AlCl, AlC13 40 1.5 Brz Clz a Reactions were run using 10% excess BrCl in chloride with a CHtClz :benzene ratio of 25.
+
Yield,
% 92 80-85 95 62 43-58 methylene
20'C In hnefhylene Chloride
0
0
I
I
I
1
I
I
I
25
50
75
100
125
150
175
Minuter
Konishi and coworkers (1968). Ethanol was oxidized quantitatively t o acetic acid in less than 3 hr a t 50' using BrCl whereas aqueous bromine gave less than 75% conversion under identical conditions. Reactions of Bromine Chloride with Aromatic Compounds
Some of the most important reactions of BrCl are electrophilic brominations of aromatic compounds. Here, the advantages of BrCl in reactivity and its formation of by-product HCl are particularly useful. The rapidity of this reaction with phenolic compounds permits its use in the analytical determination of phenols, cresols, nitrophenols, and salicylic acids (Schulek and Burger, 1958a, 1960). The product yields of several substitution reactions with BrCl are listed in Table 11. Most of these reactions were carried out in chlorinated solvents such as methylene chloride a t temperatures between 0 and 40'. The reaction of BrCl with aromatic compounds gave different results with different catalysts. The reactivity of those catalysts employed varied directly with their strength as Lewis acids (AlCl3 > FeC13 > Fe). Table I11 compares the effect of aluminum chloride and ferric chloride catalysts on both BrCl and bromine reactions. Aluminum chloride was a significantly more active catalyst than ferric chloride. For example, the preparation of hexabromobenzene by bromination of benzene using BrCl and ,41C13 required less than 25% of the time needed using FeC& as the catalyst. Using bromine and FeC13 as the catalyst, higher temperatures and longer reaction times were required to give good yields. I n monobromination of aromatics, a milder catalyst, such as elemental iron, tends to keep chlorination and by-product formation a t a minimum while increasing yields. Reactive catalysts lead to lower yields, more by-products, and chlorination. The more reactive aromatic compounds do not need catalysts. Deactivated aromatics will undergo bromination with BrCl in the presence of active catalysts with essentially no chlorination. The advantage of using preformed and more associated BrCl is also shown in Table 111. When bromine and chlorine were mixed in situ, the yields of hexabromobenzene were substantially lower Free-Radical Reactions of Bromine Chloride
I n free-radical reactions, bromine is very selective but also very unreactive compared to chlorine. Bromine chloride undergoes free-radical reactions much more easily than bromine. A surprising aspect of the reaction is the fact that alkyl bromides are formed almost exclusively with very little chloride formation. One explanation for this is t h a t the high electron density of the alkyl radical attracts the bromine end of a BrCl molecule (Walling, 1957). The reaction probably proceeds through
Figure 2. Comparison in which bromine chloride and bromine add to acrylamide. Reactions were run in the dark using 3% monomer in methylene chloride solution (Mills and Schneider, 1968)
a free-radical chain reaction mechanism as described for methane, i.e.
+ Br.
BrCl C1.
+ CHd
+ C1
--f
CH3.
+ HCl
nil
Br.
+ CHI + CH3. + HBr
CH3.
+ BrCl + CH4Br + C1.
A H , kea1 (Walling, - 13)
1957)
The positive heat of reaction for hydrogen abstraction by the bromine radical helps explain the comparatively low bromine activity as well as the tendency favoring HC1 by-product for the BrCl reaction. Some examples of free-radical reactions utilizing BrCl are
+ BrCl CBrF3 (Ruh and Davis, 1953) Cl+.3=CC1* + BrClC13C-CClzBr (Burk, 1971) CH3I + BrCl +CHzClBr + HC1 (Societa Chimica dell'CHF3
--f
dniene, 1961) The vapor-phase bromination of pyridine with BrCl has been reported to give 2-bromopyridine in 75% yield a t temperatures much lower than required by bromine (Boudakian, et al., 1967). Reactions of Bromine Chloride with Olefins
The gaseous-state reaction of bromine chloride with ethylene was studied and patented by Dow (1919). BrCl
+ CHz=CHz +CH2BrCHzC1
Later investigators established that BrCl added faster t o olefinic compounds than any other halogen or interhalogen (White and Robertson, 1939). For example, the addition of BrCl t o cis-cinnamic acid is reported t o be 400 times faster than bromine addition. A comparison in which BrCl and bromine add to acrylamide is shown in Figure 2. It was also demonstrated t h a t the addition mas like that for bromine rather than chlorine. Thus, the addition rate was first order in olefin and second order in BrC1. A detailed study of the addition reactions of BrCl was made by Buckles and Long (1951). It was concluded t h a t bromine chloride reacts as Br +-C1- and proceeds through the expected polar addition mechanism. The problem that confronts someone attempting to add BrCl t o a double bond is that, in solution or in the vapor phase, BrCl exists in equilibrium with bromine and chlorine. Therefore, instead of obtaining only the bromochloro adduct, Ind. Eng. Chern. Prod. Res. Develop., Vol. 1 2 , No. 3, 1973
163
Table IV. Comparison of the Product Ratios (Bromochloro Adduct : Dibromo Adduct) Obtained with liquid BrCl and (Br2 C12)-CC14a
+
--Mole Major product
Olefln
liquid BrCl
4 Trichloroethylene CC12BrCHClz 2 CHClBrCHC12 cis-1,2-Dichloroethylene Vinylidine CClzBrCHzCl 11 chloride Vinyl chloride CHC12CHzBr 5 Vinyl bromide CHBrC1CH2Br 6 Reactions were run at 0-5' in the dark carbon tetrachloride solution. 5
ratio-Cfi
:?; ; " '
CCI4
col 4
27 59
2 51 1 73
17 15
58
1 73
6 T
88 2 54 2 3 95 2 88 2 4 using 3°C olefin in
one finds a mixture of the bromochloro, dichloro, and dibromo adducts. Table I V contains the results obtained with a series of olefins where the ratio of the amount of bromochloro adduct formed is compared to the amount of dibromo adduct formed. I n one case liquid BrCl was used and in t h e other a solution of equimolar quantities of bromine and chlorine in carbon tetrachloride was used. I n all cases, much more bromochloro adduct was found using liquid BrC1. A reasonable explanation for these observations is the relatively high rates for the addition reaction compared to the rate of formation and equilibration of BrCI. Bromine chloride was added to the olefins in three different ways: neat, in methylene chloride solution, and in carbon tetrachloride solution. I n all cases where BrCl waq added, neat BrCl yielded higher ratios of bromochloro to dibromo adduct. Also higher ratios were found with carbon tetrachloride than with methylene chloride solutions. Thus, when a carbon tetrachloride solution of vinylidene chloride was treated with liquid BrCl, a BrC1:Brz adduct ratio of 11.6 was obtained. With methylene chloride as a solvent, the same adduct ratio was 1.4. The use of sodium chloride and water or hydrochloric acid aids in obtaining more of the bromochloro adduct by depressing t h e dissociation of BrC1. Reactions of Bromine Chloride Involving Selectivity
In some cases, it has been shown that BrCl is more selective than bromine. Dietzler and Bradley (1969) have reported that BrCl reacts with o-chlorophenol to give higher yields of 2-bromo-6-chlorophenol. -Is stated earlier, BrC1 adds OH
OH
OH
74%
22%
Br
exceptionally fast to double bonds. The reaction is so rapid that i t has been used for the determination of unsaturatioii iu a n aldehyde (Schulek and Burger, 1960). With bromine, a competitive reaction occurs in which the aldehyde is oxidized along with the addition of bromine to t'he double bond. However, the more reactive BrCl adds to t h e double bond hefore it oxidizes the aldehyde, even though BrCl is a stronger osidation agent than bromine. The addition reaction is over in less than 2 miii, so that the osidatioii reaction does not interfere. UrCl
CHzxCHCHO +CHZClCHI3rCHO 164 Ind. Eng. Chem. Prod. Res. Develop., Vol. 12, No. 3, 1973
Table V. Miscellaneous Compounds Prepared Using Bromine Chloride Starting material
Yield, Product
%
Comment
Succinimide N-Bromosuccinimide 86 a Acetamide N-Bromoacetamide 71 a Sodium cyanide Cyanogen bromide 95 6 Pyridine py BrCl complex 85 c Dioxane diox. BrCl complex 74 d Sitromethane Tribromonitromethane 88 e (CH8)dNCl (CH3)4SBrC12 95 f Dowex 1 anionPolyhalide resin 95 g exchange resin (BrCl2anion) a Reactions were run at room temperature in aqueous sodium hydroxide. * NaCN was added slowly to aqueous BrCl solution at IO". c Reaction was run at room temperature in methylene chloride using 10% excess BrC1. Schneider and Mills (1971). e Burk and Davis (1964). f Mills (1964). 0 Mills (1969).
Khen benzoyl chloride is brominated with bromine, the chlorine is displaced by a bromine and the final product is m-bromobenzoyl bromide. Bromination of benzoyl chloride with BrCl gives m-bromobenzoyl chloride without halogen exchange (Britton and Tree, 1952). Reaction of Bromine Chloride with Miscellaneous Compounds
Table V lists some miscellaneous reactions involving the use of BrCl, including the products and per cent yields of these reactions. 811 the reactions were conducted a t room temperature and generally resulted in high yields. The S-bromosuccinimide and AV-bronioacetamide were prepared in the aqueous base. Reactions of Bromine Chloride with Water
Bromine chloride appears to hydrolyze esclusively to hypobromous acid. ErC1
+ H 2 0 +HOBr + HC1
If any hydrobromic acid (HBr) were formed by hydrolysis of the dissociated bromine, it would be quickly oxidized by hypochlorous acid to hypobromous acid. HBr
+ HOC1 +HOBr + HCI
Kanyaev and Shilov (1940) have reported the hydrolysis constant for BrCl in water is 2.94 X a t 0". Thus, BrCl hydrolysis is 4000 times faster than the hydrolysis of bromine a t 0' (Liebhafsky, 1934)l. in \yater [K = 0.70 x Since the hypohalous acids are much more active disinfectants as well as hpdrobrominating agents than hypobromite ions, the effect of pH on their ionization is very important. The lower ionization value for hypobromous acid (pK = 8.70) compared to that of hypochlorous acid [pK = 7.45 (Farkas and Lewin, 1950)] contributed to t h e higher disinfectant activity of BrCl compared to chlorine reported by Kamlet (1953). For example, a t p H 8.0, a typical aqueous solution disinfected with BrCl would yield 90% of its bromine as hypobromous acid, whereas, under similar conditions, chlorine would produce only 19% hypochlorous acid. Corrosivity of Bromine Chloride toward Metals
From the corrosivity data obtained with a wide variety of metals, it would appear that any metal presently used with broniiiie would fare significantly better 1%hen used with BrCl instead (11ills and Oakes, 1973). I n comparison, dry BrCl is between 1 and 2 orders of magnitude less corrosive than dry
Table VI. Corrosion Rates (Mils per Year) (30 Days at 2 0 ” ) ~ --O% HzO---0.01% HzO--Metals
Brz
13 Low-carbon steel “SS” 316 1 None1 400 0 0 Kickel 200 a Duplicate coupons were in sealed bottles.
BrCl
0 93 7 014 0 017 46 38 0 044 50% immersed in
Brz
li
BrCl
1 75 2 2
8 8 18 0 41 0 96 0 3i the liquid halogen
bromine to various metals such as low-carbon steel, stainless steel, nickel, aiid Alonel. Under conditions where moisture is present, BrCl is not as st’rikingly superior to moist bromine, but i t is still significantly less corrosive to t h e four metals listed in Table VI. For practical comparisons, moist BrCl is less corrosive t o low carbon steel than bromine is to stainless steel or Monel 400 under similar conditions of temperature and moisture. BrCl shows no evidence of stress corrosion cracking of stainless steel n-it11 or without added moisture. Toxicity and Handling Precautions
All persons handling 13rC1should be thoroughly aware of its hazardous properties. Like bromine, liquid BrCI rapidly a t tacks the skin and other tissues, producing irritation and burris which heal very slowly, while even comparatively low coiiceiitratioris of vapor are highly irritating and painful t o the respiratory tract. When handling BrC1, operators should use neoprene rubber gloves and rubber protective clothing. K h e n vapor contact is likely, respiratory protective equipment’ should be worn. Personnel should know t,he location and use of the various pieces of protective equipment arid be instructed in first aid measures. Summary
We have attempted t o present a comparison of the chemical aiid physical properties of bromine chloride and bromine. We hope this information will furnish processors with a better understanding of this alternative method of bromiiiatioii. Bromine chloride offers cheniical processors several importaiit advantages over bromine iri such areas as chemical reactivity, selectivity, corrosivity, arid a potentially loner cost brominating agent. In many of its uses as a brominatiiig agent, BrCl contributes 40% by weight inore bromine t,liaii bromine itself. Its high reactivit’y and its almost exclusive production of hydrogeii chloride as a by-product should have a significant’impact on plant design and cost. Acknowledgment
’IYe are indebted to ,J. R. Pipal and R. E. Sturm for aid
in reactioii studies and for determining physical property data. literature Cited
Alley, E. G., Mills, J. F., unpublished material, 1972. Barratt, S., Stein, C. P., Proc. Roy. SOC.,Ser. A , 122, 582 (1929). Boudakian, bI. M., Gavin, D. F., Polak, R. J., J . Heterocycl. Chem., 4, 377 (1967). Britton, E. C., Tree, R. &I.,Jr., The Don. Chemical Co., U. S. Patent 2,607,802 (1952). Buckles, R. E., Long, J. W., J . Amer. Chem. Soc., 73, 998 (1951). Burger, K., Gauzer, F., Schulek, E., Talanta, 5 , 97 (1960). Burk, G. 4.,private communication, 1971. Burk, G. A., Davis, R. A., The Don, Chemical Co., U. S. Patent 3,159,694 (1964). Cole, L. G., Elverum, G. W., J . Chem. Phys., 20, 1543 (1952). Dietzler, A. J., Bradley, K. B., The Dow Chemical Co., U. S. Patent 3,449,443 (1969). Dow, H. H., The Don, Chemical Co., U. S. Patent 1,306,472 (1919). Emeleus, H. J., Anderson, J. S., “Modern A$pects of Inorganic Chemistry,” 3rd ed, p 452, Van Yostrand, Tu’ew York, N. Y . , 1960. Farkas, L., Lewin, &I.,J . Amer. Chem. Soc., 72, 5766 (1950). Forbes, G. S., Fuoss, R. M.,ibid., 49, 142 (1927). Glew, D. S.,Kames, D. A., private communication, 1970. Greenwood, K. Tu’., Ed., “A Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Suppl. 11,J’ol. 1, p 476, Longmans, Green and Co., London, 1956. Kamlet, J., U. S. Patent 2,662,853 (1953). Kanyaev, X. P., Shilov, E. A., Tr. Ioanov. Khim.-Tekhnol. Inst., No. 3, 69 (1940). Konishi, K., AIori, Y., Inoue, H., Nozoe, AI., Anal. Chem., 40, 2198 (1968). LaBarge, R. G., Mills, J. F., in preparation, 1973. Liebhafsky, H. A., J . Amer. Chem. SOC.,56, 1500 (1934). bIcBee, E. T., Sanford, R. A., Graham, P. J., ibid., 72, 1651 (1950). Melior, J. W., “A Comprehensive Treatise on Inorganic and Theoretical Chemistry,” Vol. 11, Suppl. I, pp 476-482, 689723, Longmans, Green and Co., London, 1956. Mills, J. F., The Dow Chemical Co., G. S. Patent 3,156,521 (1964). Slills, J. F., The Dow- Chemical Co., U. 8. Patent 3,462,363 (1969). AIills, J. F., Oakes, B. D., manuscript in preparation, 1973. Mills) J . F., Schneider, J. A . , unpublished material, 1968. Obenland, C. O., J . Chem. Edztc., 41, 506 (1964). Popov, $. I., Mannion, J. J., J . Amer. Chem. Soc., 74, 222 (1952). Ruh, R. P., Davis, R. A., The Dow Chemical Co., U. S. Patent 2,638,086 (1933). Schneider, J. A., Mills, J. F., The Dow Chemical Co., U. S. Patent, 3,607,883 (1971). Schulek, E., Burger, K., Talanta, 1, 224 (1958a). Schulek, E., Burger, K., ibid., 1, 147 (1958b). Schulek, E., Burger, K., Magy. Tiid. Akad., Kem. Tucl. Oszt. Kozlem., 12, 15 (1959). Schulek, E., Burger, K., Ann. C‘nic. Sei. Budapest. Roland0 Eotvos Sominatae, Sect. Chiin., 2 , 139 (1960). Societa Chimica dell’Aniene S.P.A., British Patent 874,062 11961). Speier, J. L., J . Amer. Chem. SOC.,73,826 (1931). Vesper, H. G., Rollefson, G. K., zbzd., 56, 620 (1934). Walling, C., “Free Radicals in Solution,” p 379, Wiley, Sew York, S. Y . , 1957. White, E. P., Robertson, P. W., J . Chem SOC.,1509 (1939). RECEIVED for review January 15, 1973 ACCEPTEDJune 18, 1973
Ind. Eng. Chem. Prod. Res. Develop., Vol. 1 2 , No. 3, 1973
165
