WO1984001380A1 - Production of phenyl carbamates - Google Patents

Production of phenyl carbamates Download PDF

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Publication number
WO1984001380A1
WO1984001380A1 PCT/GB1983/000250 GB8300250W WO8401380A1 WO 1984001380 A1 WO1984001380 A1 WO 1984001380A1 GB 8300250 W GB8300250 W GB 8300250W WO 8401380 A1 WO8401380 A1 WO 8401380A1
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Prior art keywords
phenol
amine
phosgene
phenyl
chloroformate
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PCT/GB1983/000250
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French (fr)
Inventor
Frank Hardwick
Alan Cotton
Peter Graham Spencer Field
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Staveley Chem Ltd
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Publication of WO1984001380A1 publication Critical patent/WO1984001380A1/en

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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C271/00—Derivatives of carbamic acids, i.e. compounds containing any of the groups, the nitrogen atom not being part of nitro or nitroso groups
    • C07C271/06—Esters of carbamic acids

Definitions

  • the present invention relates to the production of phenyl carbamates.
  • the invention is particularly but not exclusively concerned with the production of 2-(methyl ethoxy)-phenyl N-methyl carbamate, which is also known as propoxur.
  • Propoxur is known to have insecticidal activity.
  • the present invention aims to provide an improved method of producing phenyl carbamates, such as propoxur.
  • a method of producing a phenyl carbamate comprising reacting a phenol with phosgene to produce a phenyl chloroformate, the phosgene being present in non-aqueous inert solvent and the non-aqueous solvent being in contact with an aqueous solution of an acid acceptor to provide a two-phase system, and adding an amine to the two- phase system after the reaction of the phosgene and the phenol, the amine reacting with the chloroformate to form the phenyl carbamate.
  • the phenol dissolves in the aqueous solution and it is believed that the phenol reacts with the phosgene at the interface of the non-aqueous solvent. It would be expected that the phenyl chloro formate would be hydrolysed by the water of the aqueous solvent. Surprisingly, however, this does not occur and the phenyl chloroformate remains in the non-aqueous solvent.
  • the amine used may be primary or secondary amine.
  • the amine may be of the formula NHR'R", where each of R' and R" is a substituted or unsubstituted alkyl, aryl or aralkyl group, a hydroxy group, an alkoxy group or a hydrogen atom, at least one of R' and R" not being hydrogen.
  • the alkyl group, the alkyl group of the aralkyl group or the alkoxy group contains up to 6 carbon atoms.
  • the amine may be passed directly as a gas into the chloroformate solution or added in aqueous solution to the chloroformate solution.
  • the acid acceptor is preferably an alkali metal hydroxide, e.g. soidum hydroxide, and is preferably used in a high concentration e.g., at least 5M.
  • the non-aqueous solvent is preferably one in which the phenyl carbamate produced is insoluble or can be crystallized from.
  • the non-aqueous solvent may be toluene or, preferably cyclohexan e (C 6 H 12 ).
  • the initial phenol nay be phenol (C 6 H 5 OH) itself, a cresol or an alkoxyphenol.
  • the initial phenol is o-isopropoxy phenol and the amine used is methyl amine.
  • the amount of acid acceptor present in the aqueous solution, when the phenol carbamate is to be formed is at least two moles per mole of initial phenol.
  • Such an amount of acid acceptor is required in order to remove from the organic solution all the hydrogen chloride formed when the phosgene reacts with the phenol and the chloroformate reacts with the amine.
  • the invention provides a route to not only propoxur but other compounds which may be novel and may have insecticidal activity.
  • Example 1 gaseous methylamine was then bubbled into the mixture.
  • Example 2 an aqueous solution of amine or amine hydrochloride (0.1 mole) was added followed by further base (8M aqueous
  • the apparatus used comprised a 500 cm 3-necked round bottom flask, as a reaction vessel, fitted with a temperature indicator, water mil dry i ce conden ser and a pressure-equal ize d dropping funnel.
  • the flask was magnetically stirred and vented to a scrubber.
  • the scrubber was a caustic scrubber. In Example 4 the scrubber was at sl ight negative pressure.
  • methylamine was bubbled into the mixture in the reactor to effect amination of the chloroformate dissolved in the cyclohexane.
  • the reaction was exothermic and was taken to be completed when the temperature in the reactor peaked at around 70oC.
  • the reactor was then cooled and crystallization of a product occurred.
  • the product was filtered from the reaction system, thoroughly washed with water followed by cyclohexane and dried overnight at 50 to 60° in a vacuum oven.
  • the product was identified as propoxur by comparison of its IR spectra with that of a standard sample.
  • the product had a melting point of 90.7°C (m.p. of standard propoxur - 91°C) and was obtained in a yield of 83% based on the initial phenol.
  • the scrubber was a caustic scrubber.
  • Reagents Phosgene, o-isopropoxy phenol bp (198 760 ⁇ C ) and hydroxylamine hydrochloride.
  • Reagents Phosgene, o-isopropoxy phenol (bp 198 760 ⁇ C), aniline-'- 7% w/w HC1.
  • Reagents Phosgene, o-isopropoxy phenol, p-aminophenol (pAP) 7% HCl.
  • the product was mauve coloured, it was filtered and washed with cyclohexane and water and then vacuum dried.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

Abstract

A method of producing a phenyl carbamate, comprises reacting a phenol with phosgene to produce a phenyl chloroformate, the phosgene being present in a non-aqueous inert solvent and the non-aqueous inert solvent being in contact with an aqueous solution of an acid acceptor to provide a two-phase system, and adding a primary or secondary amine to the two-phase system after the reaction of the phosgene and the phenol, the amine reacting with the chloroformate to form the phenyl carbamate. The initial phenol may be O-isopropoxyphenol and the amine used may be methyl amine, the phenyl carbamate produced being 2-(1-methyl ethoxy)-phenyl N-methyl carbamate, also known as propoxur.

Description

Production of Phenyl Carbamates
The present invention relates to the production of phenyl carbamates.
The invention is particularly but not exclusively concerned with the production of 2-(methyl ethoxy)-phenyl N-methyl carbamate, which is also known as propoxur.
Propoxur is known to have insecticidal activity.
Various methods of producing phenyl carbamates are known.
It is known from U.S. patent specification no. 3,167,472 to produce a phenyl carbamate by reacting phenol with phosgene to produce a chloroformate and then reacting the chloroformate with an amine, these reactions being carried out in a single-phase system comprising toluene as a solvent.
It is known from British patent specification no. 1,200,768 to produce a chloroformate by reacting phenol with phosgene, the reaction being carried out in two-phase system comprising tetrachloroethylene in which the phosgene is dissolved and an aqueous solution of sodium hydroxide.
It is known from British patent specification no. 1583677 to react an isocyanate with phenol to produce a carbonate, the reaction being carried out in an inert solvent and in the presence of a base. It is also known from the same patent specification to react a phenol with a compound of formula HalCONR1R2 (where R1 is alkyl and R2 is alkyl or hydrogen) to produce a carbamate, the reaction also being carried out in an inert solvent and in the presence of a base. In particular, it is known to produce propoxur by reacting 2-isopropoxy phenol with methyl isocyanate. However, methyl isocyanate is difficult to synthesize.
We have attempted to produce propoxur by phosgenation of 2-isopropoxyphenol followed by amination of the resulting chloroformate, these reactions being carried out in toluene. However, we have not found this method satisfactory because an organic base is required to remove HCl and it is difficult to recover the base, if the organic base is an N,N-dialkylaniline (an organic base comnonly used on account of its high boiling point) the product is badly discoloured, the yield is poor and variable, and the solubility of the product in an aromatic solvent is sufficiently hign that at least part of the solvent must be distilled off to recover the product.
The present invention aims to provide an improved method of producing phenyl carbamates, such as propoxur.
In accordance with the present invention, there is provided a method of producing a phenyl carbamate, comprising reacting a phenol with phosgene to produce a phenyl chloroformate, the phosgene being present in non-aqueous inert solvent and the non-aqueous solvent being in contact with an aqueous solution of an acid acceptor to provide a two-phase system, and adding an amine to the two- phase system after the reaction of the phosgene and the phenol, the amine reacting with the chloroformate to form the phenyl carbamate.
The phenol dissolves in the aqueous solution and it is believed that the phenol reacts with the phosgene at the interface of the non-aqueous solvent. It would be expected that the phenyl chloro formate would be hydrolysed by the water of the aqueous solvent. Surprisingly, however, this does not occur and the phenyl chloroformate remains in the non-aqueous solvent.
It is believed that the amine reacts with the chloroformate at the interface of the non-aqueous solution. The carbonate dissolves in the non-aqueous solvent and may be recovered therefrom.
The amine used may be primary or secondary amine. In particular, the amine may be of the formula NHR'R", where each of R' and R" is a substituted or unsubstituted alkyl, aryl or aralkyl group, a hydroxy group, an alkoxy group or a hydrogen atom, at least one of R' and R" not being hydrogen. Preferably the alkyl group, the alkyl group of the aralkyl group or the alkoxy group contains up to 6 carbon atoms.
The amine may be passed directly as a gas into the chloroformate solution or added in aqueous solution to the chloroformate solution.
The acid acceptor is preferably an alkali metal hydroxide, e.g. soidum hydroxide, and is preferably used in a high concentration e.g., at least 5M. The non-aqueous solvent is preferably one in which the phenyl carbamate produced is insoluble or can be crystallized from.
The non-aqueous solvent may be toluene or, preferably cyclohexane (C6H12).
The initial phenol nay be phenol (C6H5OH) itself, a cresol or an alkoxyphenol.
In order to produce propoxur, the initial phenol is o-isopropoxy phenol and the amine used is methyl amine.
Preferably the amount of acid acceptor present in the aqueous solution, when the phenol carbamate is to be formed, is at least two moles per mole of initial phenol. Such an amount of acid acceptor is required in order to remove from the organic solution all the hydrogen chloride formed when the phosgene reacts with the phenol and the chloroformate reacts with the amine.
The invention provides a route to not only propoxur but other compounds which may be novel and may have insecticidal activity.
The invention is illustrated by the following examples, which were carried out on 100 milliroolar scale approximately.
Ineach of the examples, a solution of phosgene (11g, 0. 11 mole) in cyclohcxane (75 cm ) was prepared, to which was added rapidly the phenol (0.3 mole). Reaction did not occur until base (8M aqueous NaOH) hud been added when exothermic reaction began and the rate of addition of base was controlled so that the temperature was maintained ≤ 70ºC in order to avoid solvent reflux.
Sodium chloride was precipitated as the chloroformate was produced and then the excess phosgene was removed by nitrogen purging.
In Example 1 gaseous methylamine was then bubbled into the mixture. In Examples 2 to 8, an aqueous solution of amine or amine hydrochloride (0.1 mole) was added followed by further base (8M aqueous
NaOH) to act as acid acceptor in the case of water-soluble amine or to act as both acid acceptor and free base liberator in the case of hydrochloride solution.
Again reaction occurred with the evolution of heat and the formation of sodium chloride. The two-phase system was then allowed to cool and the carbamate cyrstallized. The product was then filtered and washed with water to remove any sodium chloride and finally vacuum dried.
In each example, the apparatus used comprised a 500 cm 3-necked round bottom flask, as a reaction vessel, fitted with a temperature indicator, water mil dry i ce conden ser and a pressure-equal ize d dropping funnel. The flask was magnetically stirred and vented to a scrubber.
In Examples 3 to 8, the scrubber was a caustic scrubber. In Example 4 the scrubber was at sl ight negative pressure.
Details of the examples are given below.
EXAMPLE 1 Preparation of 2-(1-methyl-ethoxy)-Phenyl N-methyl carbamate
A 15% by weight solution of phosgene in cyclohexane was prepared. An amount of this solution containing 0.11 moles of phosgene was put into a reactor. 0.1 moles of o-isopropoxyphenol was then added to the reactor. Next 0.2 moles of sodium hydroxide as an 8M aqueous solution were added slowly to the reactor. An exothermic reaction resulted from the addition of the sodium hydroxide and the rate of addition of the sodium hydroxide was controlled so as to keep the temperature in the reactor from exceeding 70°C and thereby to avoid the reflux of the solvent (b.p. of C6H12= 80.1°C).
The phosgene reacted with the phenol to produce o-phenyl chloroformate, which dissolved in the cyclohexane.
After the addition of the sodium hydroxide solution had been completed, excess phosgene was purged using nitrogen until the solution was phosgene-free and water was added to the reactor to dissolve salt which had precipitated.
Then methylamine was bubbled into the mixture in the reactor to effect amination of the chloroformate dissolved in the cyclohexane. The reaction was exothermic and was taken to be completed when the temperature in the reactor peaked at around 70ºC. The reactor was then cooled and crystallization of a product occurred. The product was filtered from the reaction system, thoroughly washed with water followed by cyclohexane and dried overnight at 50 to 60° in a vacuum oven.
The product was identified as propoxur by comparison of its IR spectra with that of a standard sample. The product had a melting point of 90.7°C (m.p. of standard propoxur - 91°C) and was obtained in a yield of 83% based on the initial phenol.
It has been found that even if the initial o-isqpropoxyphenol has impurities, the purity of the propoxur obtained is unaffected.
EXAMPLE 2
Reagents: Phosgene, o-isopropoxy phenol and methylamine
Procedure: The flask was charged with 75 cm' cyclohexane and 11g phosgene. 15.2g o-isopropoxy phenol was added rapidly with negligible temperature change followed by slow addition of 25 cm' 8M NaOH giving exothermic reaction (maximum temperature 60°C) and formation of NaCl and the chloroformate. Excess phosgene was removed using a nitrogen purge and then aqueous methylamine solution (3.1g of methylamine as a 1M solution) again giving exothermic reaction. Tmax = 41ºC. On cooling crystallization occurred giving a white product which was filtered, water wash and then vacuum dried.
Product: Yield = 65% m.pt = 90.9ºC
2(1-methyl ethoxy)phenyl N-methyl carbamate
Figure imgf000011_0001
EXAMPLE 3
The scrubber was a caustic scrubber.
Reagents: Phosgene, o-isopropoxy phenol bp (198760 ●C ) and hydroxylamine hydrochloride.
Procedure: The flask was charged with 75 cm' of cyclohexane and 11g of phosgene, 15.2g of the o-isopropoxy phenol were added rapidly with negligible temperature change, followed by 25 cm3 of 8M NaOH. Addition time was 10 minutes and the temperature rose from 22 to 61°C. A sample was taken for I.R. analysis and the characteristic absorption @ 1795 cm-1 was observed indicating conversion to chloroformate. The excess phosgene was removed by nitrogen purge. Hydroxylamine hydrochloride (6.95g) was added as a 20% w/w solution followed by 12 cm3 8M NaOH to liberate the free base. The temperature rose slowly from 17 to 36●C in seven ninutes and the reactor was allowed to cool with continued magnetic stirring. Crystallization occurred giving an off-white product which was filtered, water washed and vacuum dried.
Product: Yield = 61%
2-(1-methyl ethoxy)phenyl N-hydroxy carbamate
Figure imgf000012_0001
EXAMPLE 4
The scrubber wab » caustic scrubber at slight negative pressure.
Reagents: Ganeous phosgene, o-isopropoxy phenol (bp760198ºC) and o-methyl hydroxylamine hydrochloride
Procedure: The flask was charged with 75 cm3 cyclohexane and 11g of phosgene were added giving a 15.8% w/w solution, 15.2g of the o-isopropoxy phenol were added rapidly with negligible temperature change followed by 25 cm3 8M NaOH addition time 10 minutes and the maximum temperature 64°C. The excess phosgene was removed using a nitrogen purge and the o-methyl hy-droxylamine hydrochloride (8.35g) was added as a 20% w/w solution followed by 12.5 cm3 8M NaOH to liberate the free base. Addition took
10 minutes and the maximum temperature was 35°C. The reaction mixture was allowed to cool and crystallization occurred giving a white product, that was filtered, water washed and vacuum dried.
Product: Yield = 69% m.pt = 83.7ºC
2-(methyl ethoxy)phenyl N-methoxy carbamate
Figure imgf000013_0001
EXAMPLE 5
Reagents: Phosgene, o-isopropoxy phenol (bp 198760 βC), aniline-'- 7% w/w HC1.
Procedure: The flask was charged with 75 cm3 cyclohexane .and llg phosgene followed by 15.2g o-isopropyl phenol. 12.5 cm3 of 8M NaOH were added slowly and the temperature rose from 26 to 54°C. Excess phosgene was removed using a nitrogen purge. The solution was added rapidly with vigorous stirring to the chloroformate solution followed by 25 cm3 8M NaOH to act as acid acceptor and liberate free base. The temperature rose slowly from 22 to 37°C maximum and the solid product crystallized very suddenly giving .an off-white product which was filtered, water washed and vacuum dried.
Product: Yield = 38% m.pt = 97.4βC
2-(methyl ethoxy)phenyl N-phenyl carbamate
Figure imgf000014_0001
SUBSTITUTE SHEET
Figure imgf000014_0002
EXAMPLE 6
Reagents: Phosgene, o-isopropoxy phenol, p-aminophenol (pAP) 7% HCl.
Procedure: The flask was charged with 75 cm3 cyclohexane and 11g phosgene, 15.2g o-isopropoxy phenol were added rapidly followed by 25 cm3 8M NaOH. Temperature rose from 22 to 69°C. Excess phosgene was removed by a nitrogen purge. 10.9g pAP were added to 50 cm3 of approximately 7% HCl and the resultant hydrochloride solution was brownish. This was added rapidly followed by 12.5 cm3 8M NaOH and crystallization occurred very suddenly Tmax = 34°C.
The product was mauve coloured, it was filtered and washed with cyclohexane and water and then vacuum dried.
Product: Yield = 64% m.pt = 137.4ºC
2-(1-methyl ethoxy) phenyl N,-4-hydroxy phenyl carbamate
Figure imgf000015_0001
EXAMPLE 7
Reagents: Phosgene, 3-methyl phenol (m-cresol), methylamine
Procedure: The flask was charged with 75 cm3 cyclohexane and 11g phosgene. 10.8g m-cresol were added rapidly with no temperature change. 12.5 cm3 8M NaOH were added and the temperature rose from 26 to 65°C and salt was precipitated. The excess phosgene was removed by a nitrogen purge over a period of 30 minutes. Amination was carried out by addition 75 cm3 of a 1.5M methylamine solution followed by 12.5 cm3 8M NaOH. The temperature rose rapidly to 45°C maximum and then was allowed to cool and crystalli ne solid was isolated after filtration and water and cyclohexane washing.
Product: Yield = 39% m.pt = 80.0ºC
3-methyl phenyl N-methyl carbamate
Figure imgf000016_0001
EXAMPLE 8
Reagents: Phosgene, phenol, methylamine
Procedure: The flask was charged with 75 cm3 of cyclohexane and 11g of phosgene, 9.4g of phenol were added rapidly followed by 12.5 cm3 8M NaOH. Temperature rose from 30°C to 59ºC and sodium chloride was formed. The excess phosgene was removed by a nitrogen purge and then 75 cm3 of 1.5M methyl-amine solution were added followed by 12.5 cm3 8M NaOH. The temperature rose from 17°C to 45°C and crystallization occurred. The reactor was allowed to cool and finally chilled. A white crystallizine solid was isolated by vacuum filtration and vacuum dried.
Product: Yield = 71% m.pt = 85.2°C
Phenyl N-methyl carbamate
Figure imgf000017_0001

Claims

1. A method of providing a phenyl carbamate, comprising reacting a phenol with phosgene to produce a phenyl chloroformate, the phosgene being present in a non-aqueous inert solvent and the non-aqueous inert solvent being in contact with an aqueous solution of an acid acceptor to provide a two-phase system, and adding a primary or secondary amine to the two-phase system after the reaction of the phosgene and the phenol, the amine reacting with the chloroformate to form the phenyl carbamate
2. A method according to claim 1, wherein the amine is of the formula NHR'R", where each of R' and R" is a substituted or unsubstituted alkyl, aryl or aralkyl group, a hydroxyl group, an alkoxy group or a hydrogen atom, at least one of R' and R" not being hydrogen.
3. A method according to claim 2, wherein the alkyl group, the alkyl group of the aralkyl group, or the alkoxy group contains up to 6 carbon atoms.
4. A method according to claim 1 or 2, wherein the amine is passed as a gas into the chloroformate solution.
5. A method according to claim 1 or 2, wherein the amine is added in agueous solution to the chloroformate solution.
6. A method according to .any preceding claim, wherein the acid acceptor is an alkali metal hydroxide.
7. A method according to any preceding claim, wherein the acid acceptor is present in a concentration of at least 5M in the aqueous solution thereof.
8. A method according to any preceding claim, wherein the non-aqueous solution is one in which the phenyl carbamate is insoluble or can be crystallized from.
9. A method according to any preceding claim, wherein the non-aqueous solvent is toluene.
10. A method according to any of claims 1 to 8, wherein the non-aqueous solvent is cyclohexane.
11. A method according to any preceding claim, wherein the phenol is phenol itself, a cresol or an alkoxyphenol.
12. A method according to claim 11, wherein the alkoxy group of the alkoxyphenol contains up to 6 carbon atoms.
13. A method according to claim 12, wherein the alkoxyphenol is o-isopropoxyphenol.
14. A method according to any preceding claim, wherein the amine is methyl amine.
15. A method according to any preceding claim, wherein the amount of the acid acceptor is at least two moles per mole of the phenol to be reacted.
PCT/GB1983/000250 1982-10-05 1983-10-05 Production of phenyl carbamates WO1984001380A1 (en)

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Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1264582A (en) * 1959-06-29 1961-06-23 California Spray Chemical Corp M-alkylphenyl N-methylcarbamates and agricultural pesticide compositions containing
US4123450A (en) * 1977-09-22 1978-10-31 Fmc Corporation Process for preparing alkyl isocyanates

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1264582A (en) * 1959-06-29 1961-06-23 California Spray Chemical Corp M-alkylphenyl N-methylcarbamates and agricultural pesticide compositions containing
US4123450A (en) * 1977-09-22 1978-10-31 Fmc Corporation Process for preparing alkyl isocyanates

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