CA1042923A - Production of bromostyrene, dibromostyrene and alkyl bromides - Google Patents
Production of bromostyrene, dibromostyrene and alkyl bromidesInfo
- Publication number
- CA1042923A CA1042923A CA290,898A CA290898A CA1042923A CA 1042923 A CA1042923 A CA 1042923A CA 290898 A CA290898 A CA 290898A CA 1042923 A CA1042923 A CA 1042923A
- Authority
- CA
- Canada
- Prior art keywords
- bromoethyl
- bromostyrene
- bromobenzene
- products
- bromo
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C17/00—Preparation of halogenated hydrocarbons
- C07C17/093—Preparation of halogenated hydrocarbons by replacement by halogens
- C07C17/16—Preparation of halogenated hydrocarbons by replacement by halogens of hydroxyl groups
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C17/00—Preparation of halogenated hydrocarbons
- C07C17/25—Preparation of halogenated hydrocarbons by splitting-off hydrogen halides from halogenated hydrocarbons
Landscapes
- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
Abstract
Abstract of the Disclosure A pyrolytic process for the simultaneous production of bromo-styrene and an alkyl bromide, which comprises reacting bromoethyl bromo-benzene with a lower alkanol in the absence of an alkali metal catalyst at an elevated temperature in the range of about 400° to about 550°C.
Description
: ( ``\
~4~9Z3 ;
This application is a division of application serial No.
179,044, filed August 17, 1973.
In U.S. Patent ~o. 3,737,469 issued June 5, 1973, there is described and claimed a process for the simultaneous production of bromo-styrene and methyl bromide which comprises reacting ~ -bromoethyl bromobenzene or ~ -bromoethyl bromobenzene ("the substrate") and methanol in a medium of certain molten inorganic salts.
A known process for the production of bromostyrene comprises effecting a dehydration of the respective bromophenyl methyl carbinol, or the respective bromophenyl ethyl alcohol. Another known process is the dehydrobromination of either of the respective A - or ~ -haloethyl mono-bromobenzene isomers.
This latter method is exemplified in British Patent No. 986,634.
The dehydrobromination of bromoethyl halobenzenes is effected by passing a mixture of the reactants together with an excess of steam over granular calcium sulfate catalyst. The use of calcium sulfate as catalyst is also mentioned in U.S. Patent No. 2,485,524 in vapor-phase dehydrohalogenations of substituted halo-benzenes. Other catalysts mentioned in the literature for dehydrohalogenations are calcium chloride, calcium oxide, calcium phosphate and various aluminas.
When applied to bromoethyl bromobenzene, all of these catalysts exhibit the serious drawback of causing the formation and deposition on the catalyst of tarry substances, most probably comprising a polymer formed from the monomeric bromostyrene which is the primary product of the catalytic dehydrohalogenation. The formation of the polymer cannot be avoided, even ~; when a large excess of an inert diluent, such as steam or nitrogen, is fed together with the substrate into the reaction zone. The deposition of the polymer on the catalyst reduces rapidly its activity and thus frequent , .
catalyst regenerations are required. If the catalyst is discarded after `
~04Z92~
relatively brief runs, the recharging with fresh catalyst is a compara-tively expensive operation.
To eliminate the deposition of the tarry byproducts on the fixed bed of the catalyst, a process is described in French patent No.
1,576,909, wherein the active catalyst as well as the reaction medium com-prises certain mixtures of molten salts, and in particular mixtures containing bivalent metal chlorides, such as copper chloride, in combina-tion with other salts which decrease the melting point of the salt mixture.
While according to the above disclosure it is possible to obtain, for example, high yields of vinyl chloride by the elimination of hydrogen chloride from ethylene dichloride, the said process produces only poor yields of monomers in the case of heavy, relatively non-volatile substrates. In particular, when the substrates according to the present invention are used, the conversion to the respective products is far from complete.
In U.S. Patent No. 3,737,469 a process was described whereby molten salts were used very efEectively as reaction medium for the pro-duction of bromostyrene by passing through this medium the said substrate together with a reactive diluent, such as an aliphatic alcohol, and in particular methyl alcohol. The term "reactive diluent" designates a suitable substance which acts as an acceptor - or scavenger - for the hydrogen halide which is eliminated from the substrate during the reaction.
It is believed that the fast reaction of the "reactive diluent"
with the eliminated hydrogen halide has a pronounced beneficial effect on the yield of the desired product for two reasons. It is know that elimina-tion of hydrogen halide from the substrate is a reversible reaction. If it is carried out in the presence of an acceptor for the hydrogen halide that is being eliminated - the equilibrium is shifted in the direction of the product, and the process can thereby be carried out at temperatures that are substantially lower than in the absence of the acceptor. This has ~4~a~3 the effect of increasing the selectivity of the reaction with respect to the desired product.
The enhanced selectivity of the reaction, which is achieved in the presence of the "reactive diluent" is believed to be a consequence also of the prompt removal of the hydrogen halide from the system, since this is known to catalyze the polymerization of vinylic monomers to produce oligomeric materials, which are highly undesirable.
Another advantage in use of "reactive diluents" is the rational utilization of the bromi~e.
By reacting the hydrogen bromide, which is eliminated from the bromoethyl - bromobenzene, with the "reactive diluent", useful and highly valued by-products are directly obtained instead of hydrobromic acid, which has a lower "bromine value".
As "reactive diluents" may be employed lower aliphatic alcohols and the by-products are the respective alkyl halides. When methanol is used in conjunction with the substrate, methyl bromide is obtained in quantita-tive yield. Whell ethyl alcohol is used the resulting by-product is ethyl bromide. These are widely used as soil sterilizors and fumigants, as well as fire extinguishing agents.
While results according to U.S. Patent No. 3,737,469 are generally satisfactory - the sald process has certain insufficiencies such as for instance the need for special materials of construction to be used for the reactors containing highly corrosive molten salts. Another drawback of said process is in the high ratio of reactor-space to product produced in unit time (low space-time yields).
A further drawback is the formation of small quantities of saturated products such as ethyl bromobenzenes. These products have boiling points very close to that of bromostyrene, and it is therefore very difficult to separate them by fractional distillation. Furthermore, these products are not polymerizable and even act as chain transfer agents, thus decreasing the molecular weight of the produced polymers. According to the present invention a high purity monomer is obtained albeit the conversions are lower than in the aforementioned patent.
The present invention relates to a process for the production of either bromostyrene or dibromostyrene, together with an alkyl bromide, by reacting bromoethyl bromobenzene or bromoethyl-dibromobenzene, respect-ively, with a lower alkanol at an elevated temperature in the gaseous phase and in the absence of alkali metal catalyst. The reaction is a pyrolysis reaction, and is advantageously effected at a temperature in the range of about 400 to about 550 C.
Bromostyrene is a reactive monomer which can be polymerized to a hard, transparent plastic which has many uses. It can be copolymerized with other monomers to result in copolymers which are fire retardant and self-extinguishing. It is of particular interest as a reactive component in unsaturated polyester compositions, to result in self-extinguishing transparent plastic compositions, that do not become discolored upon pro-longed exposure to weather conditions.
The term "bromostyrene" as used herein means para-bromo meta-bromo, or ortho-bromo-styrene or a mixture of any of these. It will henceforth be termed "the product".
Bromostyrene is a well-known monomer, being either a para-meta-, or ortho-bromo derivative, or a mixture of these.
The advantage of the pyrolytic method over the catalytic method described in the British Patent No. 986,634 is that in the pyrolytic method the reaction tube used for pyrolysis can be easily cleaned from any tars formed during the reaction by simply burning them by passing air through the hot reactor.
Fuller details of the present invention are described in the-following examples to which, however, it is not limited.
, Example 1~ Z3 300 g ~-bromoethyl-bromo-benzene were added through a motor driven syringe into the reactor at a rate of 60 g/h. Methanol was added at a rate of 14 g/h and nitrogen gas preheated to 300C at a rate of
~4~9Z3 ;
This application is a division of application serial No.
179,044, filed August 17, 1973.
In U.S. Patent ~o. 3,737,469 issued June 5, 1973, there is described and claimed a process for the simultaneous production of bromo-styrene and methyl bromide which comprises reacting ~ -bromoethyl bromobenzene or ~ -bromoethyl bromobenzene ("the substrate") and methanol in a medium of certain molten inorganic salts.
A known process for the production of bromostyrene comprises effecting a dehydration of the respective bromophenyl methyl carbinol, or the respective bromophenyl ethyl alcohol. Another known process is the dehydrobromination of either of the respective A - or ~ -haloethyl mono-bromobenzene isomers.
This latter method is exemplified in British Patent No. 986,634.
The dehydrobromination of bromoethyl halobenzenes is effected by passing a mixture of the reactants together with an excess of steam over granular calcium sulfate catalyst. The use of calcium sulfate as catalyst is also mentioned in U.S. Patent No. 2,485,524 in vapor-phase dehydrohalogenations of substituted halo-benzenes. Other catalysts mentioned in the literature for dehydrohalogenations are calcium chloride, calcium oxide, calcium phosphate and various aluminas.
When applied to bromoethyl bromobenzene, all of these catalysts exhibit the serious drawback of causing the formation and deposition on the catalyst of tarry substances, most probably comprising a polymer formed from the monomeric bromostyrene which is the primary product of the catalytic dehydrohalogenation. The formation of the polymer cannot be avoided, even ~; when a large excess of an inert diluent, such as steam or nitrogen, is fed together with the substrate into the reaction zone. The deposition of the polymer on the catalyst reduces rapidly its activity and thus frequent , .
catalyst regenerations are required. If the catalyst is discarded after `
~04Z92~
relatively brief runs, the recharging with fresh catalyst is a compara-tively expensive operation.
To eliminate the deposition of the tarry byproducts on the fixed bed of the catalyst, a process is described in French patent No.
1,576,909, wherein the active catalyst as well as the reaction medium com-prises certain mixtures of molten salts, and in particular mixtures containing bivalent metal chlorides, such as copper chloride, in combina-tion with other salts which decrease the melting point of the salt mixture.
While according to the above disclosure it is possible to obtain, for example, high yields of vinyl chloride by the elimination of hydrogen chloride from ethylene dichloride, the said process produces only poor yields of monomers in the case of heavy, relatively non-volatile substrates. In particular, when the substrates according to the present invention are used, the conversion to the respective products is far from complete.
In U.S. Patent No. 3,737,469 a process was described whereby molten salts were used very efEectively as reaction medium for the pro-duction of bromostyrene by passing through this medium the said substrate together with a reactive diluent, such as an aliphatic alcohol, and in particular methyl alcohol. The term "reactive diluent" designates a suitable substance which acts as an acceptor - or scavenger - for the hydrogen halide which is eliminated from the substrate during the reaction.
It is believed that the fast reaction of the "reactive diluent"
with the eliminated hydrogen halide has a pronounced beneficial effect on the yield of the desired product for two reasons. It is know that elimina-tion of hydrogen halide from the substrate is a reversible reaction. If it is carried out in the presence of an acceptor for the hydrogen halide that is being eliminated - the equilibrium is shifted in the direction of the product, and the process can thereby be carried out at temperatures that are substantially lower than in the absence of the acceptor. This has ~4~a~3 the effect of increasing the selectivity of the reaction with respect to the desired product.
The enhanced selectivity of the reaction, which is achieved in the presence of the "reactive diluent" is believed to be a consequence also of the prompt removal of the hydrogen halide from the system, since this is known to catalyze the polymerization of vinylic monomers to produce oligomeric materials, which are highly undesirable.
Another advantage in use of "reactive diluents" is the rational utilization of the bromi~e.
By reacting the hydrogen bromide, which is eliminated from the bromoethyl - bromobenzene, with the "reactive diluent", useful and highly valued by-products are directly obtained instead of hydrobromic acid, which has a lower "bromine value".
As "reactive diluents" may be employed lower aliphatic alcohols and the by-products are the respective alkyl halides. When methanol is used in conjunction with the substrate, methyl bromide is obtained in quantita-tive yield. Whell ethyl alcohol is used the resulting by-product is ethyl bromide. These are widely used as soil sterilizors and fumigants, as well as fire extinguishing agents.
While results according to U.S. Patent No. 3,737,469 are generally satisfactory - the sald process has certain insufficiencies such as for instance the need for special materials of construction to be used for the reactors containing highly corrosive molten salts. Another drawback of said process is in the high ratio of reactor-space to product produced in unit time (low space-time yields).
A further drawback is the formation of small quantities of saturated products such as ethyl bromobenzenes. These products have boiling points very close to that of bromostyrene, and it is therefore very difficult to separate them by fractional distillation. Furthermore, these products are not polymerizable and even act as chain transfer agents, thus decreasing the molecular weight of the produced polymers. According to the present invention a high purity monomer is obtained albeit the conversions are lower than in the aforementioned patent.
The present invention relates to a process for the production of either bromostyrene or dibromostyrene, together with an alkyl bromide, by reacting bromoethyl bromobenzene or bromoethyl-dibromobenzene, respect-ively, with a lower alkanol at an elevated temperature in the gaseous phase and in the absence of alkali metal catalyst. The reaction is a pyrolysis reaction, and is advantageously effected at a temperature in the range of about 400 to about 550 C.
Bromostyrene is a reactive monomer which can be polymerized to a hard, transparent plastic which has many uses. It can be copolymerized with other monomers to result in copolymers which are fire retardant and self-extinguishing. It is of particular interest as a reactive component in unsaturated polyester compositions, to result in self-extinguishing transparent plastic compositions, that do not become discolored upon pro-longed exposure to weather conditions.
The term "bromostyrene" as used herein means para-bromo meta-bromo, or ortho-bromo-styrene or a mixture of any of these. It will henceforth be termed "the product".
Bromostyrene is a well-known monomer, being either a para-meta-, or ortho-bromo derivative, or a mixture of these.
The advantage of the pyrolytic method over the catalytic method described in the British Patent No. 986,634 is that in the pyrolytic method the reaction tube used for pyrolysis can be easily cleaned from any tars formed during the reaction by simply burning them by passing air through the hot reactor.
Fuller details of the present invention are described in the-following examples to which, however, it is not limited.
, Example 1~ Z3 300 g ~-bromoethyl-bromo-benzene were added through a motor driven syringe into the reactor at a rate of 60 g/h. Methanol was added at a rate of 14 g/h and nitrogen gas preheated to 300C at a rate of
2 l/h. The reactor was a glass spiral made of a 6 mm wide 3 m long glass tube connected to a tube 30 mm wide and 25 cm long. The reactor was kept at a temperature of 490-500 C. The liquid products were collected in a trap submerged in an ice bath while the methylbromide was trapped in a receptacleplaced in liquid nitrogen. The liquid products were then sub-jected to fractional distillation in a vacuum to obtain 166 gr bromostyrene and 45 gr unconverted ~ -bromo-bromoethyl benzene. The yield is 94%
based on reacted bromoethyl bromo-benzene, 90% yield of methyl bromide was also obtained.
Example 2:
The experiment was carried out in the manner described in Example 1, but without methanol. The conversion was only 74% and the yield was only 44%. ~ substantial quantity of heavy products and tar-like materials were obtained.
Example 3:
170g ~ -bromoethyl dibromobenzene (being mainly a mixture of the ortho and para isomers) were driven into the reactor described in Example 1 at a rate of 20 gr/h together with methanol at a rate of 4.4 grlh and preheated nitrogen at a rate of 2 l/h. The products were distilled in vacuum and consisted of 14 gr unconverted product and 108 gr. dibromo-styrene, namely 91% yield.
based on reacted bromoethyl bromo-benzene, 90% yield of methyl bromide was also obtained.
Example 2:
The experiment was carried out in the manner described in Example 1, but without methanol. The conversion was only 74% and the yield was only 44%. ~ substantial quantity of heavy products and tar-like materials were obtained.
Example 3:
170g ~ -bromoethyl dibromobenzene (being mainly a mixture of the ortho and para isomers) were driven into the reactor described in Example 1 at a rate of 20 gr/h together with methanol at a rate of 4.4 grlh and preheated nitrogen at a rate of 2 l/h. The products were distilled in vacuum and consisted of 14 gr unconverted product and 108 gr. dibromo-styrene, namely 91% yield.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for the simultaneous production of bromostyrene and of an alkyl bromide, which comprises reacting bromoethyl bromobenzene with a lower alkanol in the absence of alkali metal catalyst at a temperature in the range of about 400° to about 550°C. so as to result in the desired conversion.
2. A process as claimed in claim 1, wherein a carrier gas is admixed with the reactants.
3. A process as claimed in claim 2, wherein the gas is nitrogen.
4. A process as claimed in claim 1, wherein the alkanol is methanol and one of the products is methyl bromide.
5. A process as claimed in claim 1, wherein the alkanol is ethanol and one of the products is ethyl bromide.
6. A process as claimed in claim 1, wherein the starting material is selected from .alpha.-bromoethyl bromobenzene and .beta.-bromoethyl bromobenzene.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2339612A DE2339612C2 (en) | 1973-08-04 | 1973-08-04 | Process for the simultaneous production of bromostyrene or dibromostyrene and an alkyl bromide |
| CA179,044A CA1032183A (en) | 1973-08-04 | 1973-08-17 | Production of bromostyrene, dibromostyrene and alkyl bromides |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1042923A true CA1042923A (en) | 1978-11-21 |
Family
ID=25667329
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA179,044A Expired CA1032183A (en) | 1973-08-04 | 1973-08-17 | Production of bromostyrene, dibromostyrene and alkyl bromides |
| CA290,898A Expired CA1042923A (en) | 1973-08-04 | 1977-11-15 | Production of bromostyrene, dibromostyrene and alkyl bromides |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA179,044A Expired CA1032183A (en) | 1973-08-04 | 1973-08-17 | Production of bromostyrene, dibromostyrene and alkyl bromides |
Country Status (2)
| Country | Link |
|---|---|
| CA (2) | CA1032183A (en) |
| DE (1) | DE2339612C2 (en) |
-
1973
- 1973-08-04 DE DE2339612A patent/DE2339612C2/en not_active Expired
- 1973-08-17 CA CA179,044A patent/CA1032183A/en not_active Expired
-
1977
- 1977-11-15 CA CA290,898A patent/CA1042923A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| CA1032183A (en) | 1978-05-30 |
| DE2339612A1 (en) | 1975-02-20 |
| DE2339612C2 (en) | 1982-05-19 |
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