It is well known that carbamates may be used for the protection of crops from insect attacks. Specifically it is known that N-methyl carbamates may be used for this purpose.

It is also known that there are specific problems associated with the production of N-methyl carbamate insecticides. Generally a hydroxy-containing moiety is reacted with methyl isocyanate in a solvent and generally in the presence of a base to produce the desired product. Nonetheless, there are various unwanted side products that are produced, including the molecule trimethylisocyanurate (or methyl isocyanate trimer) and various other ureas including 1,3-dimethylurea..

Furthermore, it is generally accepted in the art of carbamate production that heating a carbamate to about 150°C causes decomposition of the carbamate back to its parent constituents, the hydroxy-containing compound and methylisocyanate. This decomposition further increases the rate of formation of trimethylisocyanurate and increases the impurity profile of the product. This reverse reaction is catalysed by base.

The purity of the carbamate also generally depends on the purity of the hydroxy-containing compound. Whenever an impurity is introduced into the process from the start of the reaction, the said impurity is generally expected in the product mixture and thus will have to be purified. One consequence is that an impure product may affect the effectiveness of the final product when used commercially.

An object of the present invention is to provide an improved process for the production of an N-methyl carbamate.

Another object of the present invention is provide a process for the production of N-methyl carbamates that is substantially superior to the prior art.

Another object of the present invention is to provide a process for the production of N-methyl carbamates that substantially avoids production of unwanted byproducts.

Another object of the present invention is to provide a process for the production of N-methyl carbamates that substantially avoids production of trimethyl isocyanurate.

Another object of the present invention is to provide a process for the production of N-methyl carbamates that avoids a subsequent of simultaneous purification step.

These objects are met in whole or in part by the present invention.

The present invention provides a process for preparing an N-methyl carbamate which comprises reacting a composition consisting essentially of a hydroxy- containing compound and N-methyl isocyanate at a temperature and pressure effective to maintain the said compound in the liquid state during the reaction. The reaction mixture comprises substantially no solvent, for example less than 1% by weight of the reaction mixture, preferably less than 0.5% by weight, more preferably less than 0.1% by weight.

Generally the reaction mixture contains substantially no base or basic substance. Preferably the reaction mixture is generally pH 7 or less.

Generally the hydroxy-containing-compound is a solid at ambient temperature and ambient pressure. Generally the temperature of the process is at least the melting point of the hydroxy-containing-compound at ambient pressure. The temperature of the process is preferably greater to than 80°C, more preferably greater than 125°C, even more preferably greater than or equal to 150°C.

Generally the pKa of the proton of the hydroxy moiety of the hydroxy- containing moiety is from 8 to 11 relative to water. Preferably the hydroxy- containing-compound is a phenol or has an aryloxy group. Most preferably, the compounds that may be used in the process of the present invention are a-napthol; 2- 3-dihydro-2-2-dimethyl-7-hydroxybenzofuran; 2,2-dimethyl-4-hydroxy-1,3- benzodioxole; or 3,5-dimethyl-4-methylthiophenol.

Generally the hydroxy-containing-compound is not required to be extremely pure in order for the reaction to proceed to completion and deliver a substantially extremely high yield with little to no byproduct and little starting compound remaining. Generally the process of the invention provides from 95% to 100% conversion of the compound to the carbamate, preferably from 97% to 99%

conversion. In the case of a-napthol, the conversion is about 99% or higher with less than 1% impurities.

A further feature of the invention is that the hydroxy-containing-compound generally is mixed with methylisocyanate in a stoichiometric ratio of from 1: 1 to 1: 20, preferably from 1: 2 to 1: 15, most preferably from 1: 3 to 1: 12. This excess of methylisocyanate is present in order to maintain a positive partial pressure of methylisocyanate.

Another feature of the present invention is that the temperature of the reaction mixture is allowed to rise after introduction of the methylisocyanate. Generally, the temperature may be allowed to rise from 10 to 40 degrees centigrade. To persons skilled in the art, the maximum temperature during addition is generally known as the peak temperature of the reaction. Such a high peak temperature generally ensures that the reaction proceeds in very good conversion.

The process may be carried out in a batch process of a continuous process.

The process generally is continued until the hydroxy-containing compound is consumed.

A further feature of the invention is that there may be a subsequent cooling step to ambient temperature. This may be followed by a washing step. The said washing step provides a wash of the reaction mixture to substantially remove contaminents from the reactor vessel.

It has been surprisingly found that the N-methyl carbamates formed by the process of the present invention are of generally uniform density whereas processes of the prior art provide non-uniform densities of products. The density of the carbamates produced is generally greater than that of the prior art.

Products formed by the process of the present invention include carbaryl, carbofuran, methiocarb and bendiocarb.

The following non-limiting examples illustrate the invention.

EXAMPLE 1 a-napthol of greater than 99% purity (2.9g, 0.20 mol) and methyl isocyanate (1.3 mL, 0.022 mol) were added to a pressure vessel and the sealed vessel heated to

about 150°C over thirty minutes followed by ten minutes at 150°C. The vessel was cooled to room temperature and the 1-naphthyl methylcarbamate collected. The product was analysed to be greater than 99% pure and in greater than 99% yield. No purification of the 1-naphthyl methylcarbamate was necessary.

EXAMPLE 2 The experiment of Example 1 is repeated with a-napthol of less than 90% purity. The resulting 1-naphthyl methylcarbamate is greater than 99% pure.

EXAMPLE 3: In a four (4) liter reactor 5 molar equivalents of methyl isocyanate were added to one molar equivalent of molten 1-Naphtol in mixer type equipment over about 30 minutes. At the beginning of the addition, the temperature of the mixture was about 150°C. During the addition, the temperature was allowed to rise to about 170°C and allowed to stir an additional 15 minutes. After completion of the reaction the medium was cooled down to allow the product of the reaction to solidify and to be dispersed as a powder by the mixer agitation. Excess methylisocyanate was removed under vacuum and the remaining dry 1-naphthyl methylcarbamate discharged after cooling to room temperature. The product was generally acceptable for use in agriculture.

No solvent nor purification step was needed. There are trace amounts of impurities such as the said various ureas. The isolated yield was greater than 98% based on 1- napthol. The density of the product produced by the recited method is generally more uniform and greater than that produced by prior art methods.