Method for making carbamates

A process for the manufacture of alkyl carbamates from urea and aliphatic alcohols. The process is carried out under a vacuum, preferably at least 20 inches, and preferably in the presence of magnesium oxide catalyst.

The present invention relates to the manufacture of alkyl carbamates from 
urea and aliphatic alcohols. In accordance with the invention, a vacuum is 
applied, and preferably a magnesium catalyst is used. The vacuum 
significantly accelerates the reaction, thereby reducing the cost of 
manufacture. 
BACKGROUND OF THE INVENTION 
Alkyl carbamates are useful as intermediates for making textile 
cross-linking resins and as intermediates in the manufacture of 
pharmaceuticals. A number of procedures for manufacturing them have been 
described, e.g., in U.S. Pat. No. 3,574,711. In particular, it is known to 
manufacture them by reaction of urea with an aliphatic alcohol according 
to the reaction: 
EQU R--OH+NH.sub.2 CONH.sub.2 .fwdarw.ROCONH.sub.2 +NH.sub.3 
U.S. Pat. No. 2,837,571 describes the use or cupric salts as catalysts for 
this reaction. U.S. Pat. No. 3,574,711 discloses the possibility of 
conducting the reaction without a catalyst and also the use of zinc 
catalysts such as zinc acetate, zinc formate, zinc carbonate, or zinc 
oxide. These prior patents disclose heating the reactants at elevated 
temperatures such as 110.degree. to 200.degree. C. at atmospheric 
pressure. Liberated ammonia may be collected, e.g., in a dry ice trap. 
Following completion of the reaction, the products are recovered by 
distillation, e.g., under vacuum. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, it has been found that the 
application of vacuum to the reaction accelerates the reaction when 
carried out either without catalyst or using catalyst described 
previously. Furthermore, it has been found that the reaction can be 
accelerated by magnesium compounds. The use of vacuum when magnesium 
compounds are employed, has produced an especially useful effect. 
DETAILED DESCRIPTION 
The invention is applicable to a wide variety of alcohols i.e., alcohols 
having the formula R(OH).sub.n wherein R is an organic group and n is a 
whole number. R may be an aliphatic group, saturated or unsaturated, or it 
may be aromatic or arylaliphatic. However, the invention is particularly 
applicable to higher alcohols which are not excessively volatile under the 
temperature and pressure conditions applied in the reaction. For example, 
using a vacuum of 28 inches, isopropyl alcohol was found to be too 
volatile. The invention is applicable to alcohols containing one, or more 
than one, hydroxyl group. The invention is particularly useful with 
diethylene glycol, whose carbamate is particularly suited for the 
manufacturing of textile resins. 
The vacuum applied should be sufficient to accelerate the rate of reaction. 
In this specification, vacuum is given in inches of mercury.) A vacuum of 
10 inches or more may be used. It has been found, however, that at 10 
inches, the condenser used to trap entrained alcohol became clogged with a 
solid, which may be ammonium carbamate. This problem was not encountered 
at higher vacuums, such as 20-28 inches. Especially useful results may be 
achieved at 28 inches, although it is believed that still higher vacuums 
may be beneficial and economically useful. 
The vacuum selected must be related to the vapor pressure of the alcohol 
which may be affected by dissolved urea and/or carbamate. If the vapor 
pressure is too high, the alcohol may be entrained with escaping ammonia 
to an excessive degree. To some extent this problem may be controlled by 
passing the effluent from the reaction through a condenser which traps 
alcohol, and the trapped alcohol may be returned to the reaction vessel. 
However, too high a vacuum may, in the case of some alcohols, cause too 
much entrainment. 
One of the advantages of the present invention is that it may be carried 
out at molar ratios of urea to alcohol that are very nearly 1:1. Using 
such ratios, a relatively uncontaminated product may be obtained directly, 
with little or no need for purification. The preferred ratio is 1.1 moles 
urea for each mole of alcohol. However, it will be appreciated that other 
ratios may be used, including excess of either alcohol of urea. The 
temperature of the reaction has not been found to be critical. Initially, 
a temperature of 150.degree. C. was thought to be preferable, but a 
temperature of 160.degree. C. is now preferred. Still higher temperatures 
may be used, e.g., up to 200.degree. C. However, the increased rate of 
reaction achieved must be evaluated against the increased energy cost of 
such high temperatures. Conversely, lower temperatures may be used, e.g., 
down to 130.degree. C., although slower reactions result from lower 
temperatures. 
The process under vacuum may be conducted with no catalyst. However, the 
reaction speed is increased with catalyst. Conversely, the proportion of 
the starting materials which react in a selected cycle time is increased 
with catalysts. 
A preferred catalyst is a magnesium compound, especially magnesium oxide. 
Magnesium oxide is supplied in various grades, according to reactivity, 
which in turn depends on degree of calcination. The grades are 
characterized by the speed with which they neutralize acid. The grades are 
understood to differ in their degree of calcination, hardness and 
granularity. For purposes of the present invention, high reactivity types 
are preferred. Particularly useful is Magox 98HR, supplied by Basic 
Chemicals, a division of Basic Incorporated, Cleveland, Ohio. It is 
characterized by the following properties: 
CHEMICAL COMPOSITION 
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Typical 
Minimum Maximum 
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Analysis 
Loss on Ignition at 1370.degree. C. 
5.0% 6.0% 
Iodine No., meq/100 gms 
45 35 
Chloride (as Cl) 0.2% 0.4% 
Sulfate (as SO.sub.3) 
0.55% 0.7% 
Loss Proc Basis 
MgO 97.1% 97.0% 
CaO 1.8% 2.0% 
SiO.sub.2 0.6% 0.9% 
R.sub.2 O.sub.3 0.5% 
PHYSICAL PROPERTIES 
Sizing 99.0%-200 mesh* 
Bulk Density, Loose (approximate) 
25 lbs./ft. 3 
Cubic Displacement of 50 lb. Bag 
1.6 ft. 
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*Also available 99%-325 mesh 
Other catalysts which may be used are calcium and zinc compounds such as 
calcium oxide and zinc oxide. 
The amount of catalyst used should be sufficient to increase the rate of 
reaction. On the other hand, excessive amounts should be avoided, so as to 
minimize contamination of the product. The amount required for any 
particular reaction can be determined readily by a set of experiments 
using progressively increased amounts of catalysts. 
The reaction may be carried out in a stirred flask or other reaction vessel 
with the required amount of urea and alcohol added at the start. The 
reactants are heated with steady heat until a desired reaction temperature 
such as 150.degree. C. or 160.degree. C. is achieved. The reaction can be 
followed, e.g. by measuring either ammonia evolution or unreacted urea. 
The flask preferably is fitted with a water cooled condenser to trap 
entrained alcohol so that it can be returned to the flask. 
The carbamates are liquid at the reaction temperature. Therefore they may 
be recovered by pouring into a container and allowed to solidify. 
The following examples illustrate the practice of the invention. Unless 
otherwise indicated, parts and percentages are by weight.