DE924928C - Process for the production of formamide - Google Patents

Description

Process for Making Formamide The invention relates to on the production of formamide from alkyl formates and ammonia.

It is known that formamide when exposed to ammonia on Forms alkyl formate. According to one embodiment of a known method of manufacture Formamide converts liquid ammonia to alkyl formates in the cold, e.g. B. at -4o °, allowed to act. According to another embodiment of this method, the Reaction with compressed gaseous ammonia at pressures of 8 to 150 atm. performed. Working at ordinary pressure with liquid ammonia has the Disadvantage that at very low temperatures, at least below -33.5 ° ', the boiling point of liquid ammonia at ordinary pressure. On the other hand, it is working with gaseous ammonia under increased pressure with complicated apparatus, such as pressure-resistant conversion vessels, control valves, pressure generators, and thus high costs tied together.

The invention avoids these disadvantages in that one alkyl formate and anhydrous gaseous ammonia at ordinary pressure and Temperatures below 6o @ ° 'in a mixture which from the outset consists of formamide and an aliphatic alcohol or these substances in addition to inert solvents contains. As known inert solvents, for. B. hydrocarbons, such as benzene, or hydrogenated naphthalenes or ethers, e.g. B. dioxane can be used.

It has been shown that in the presence of formamide and aliphatic Alcohols and with the exclusion of water the implementation of the Alkyl formate with gaseous ammonia very quickly and almost completely even without higher pressures and temperatures takes place. Is z. B. methyl formate of an equimolecular mixture of formamide and methyl alcohol are added and gaseous ammonia is added to the mixture initiated, this is rapidly absorbed with the development of heat after the following Reaction: HGOOCH3 -i- NH3 = HCONH2 -; - CH30H. The reaction components settle in the process at ordinary temperature almost instantaneously up to 97%. Then the Response is slower and it takes a few hours for the remaining 3% to settle still implement. Instead of equimolecular amounts of formamide and alcohol you can also use the use one or the other starting material in excess.

The equilibrium of conversion is not very much influenced by a change in temperature within 10: to 60 °. At ao "the equilibrium corresponds to almost 99% formamide and 1% methanol. At higher temperatures, e.g. 6d °, the solubility of the ammonia is reduced, but the rate of conversion is increased. If one works, for example, at 60 °, so It is necessary to introduce the starting materials in smaller amounts than is the case at low temperatures, because otherwise the ammonia can escape because of the reduced solubility without reacting with formate. The results at 3o to 35 '° are more satisfactory than at 6o' ° '. However, the best results are obtained at even lower temperatures, e.g. B. at 1o to 2o °, achieved.

The process can be carried out continuously with particular advantage are by adding equimolecular amounts of alkyl formate, e.g. B. methyl formate, and gaseous Ammonia continuously z. B. be introduced into a column containing a mixture from formamide and an aliphatic alcohol, e.g. B. methyl alcohol, contains and the is cooled with the appropriate known means to avoid undesirable temperature increases to prevent. The reaction products can be withdrawn from the column above, collected and immediately distilled, recovering the excess alcohol is and as a distillation residue prak. pure formamide remains behind. That In addition to the alcohol, distillate contains small amounts of unreacted formate and ammonia, possibly also small amounts of formamide, but that with his immediate reuse are only beneficial for implementation.

It has been found to be useful., The reaction mixture after completion the reaction for a while, e.g. B. for a few hours to allow the reaction to complete. The distillation becomes practical only after this Make time. But you can also use the distillate, which is still not in small amounts contains converted formamide and ammonia as well as small amounts of formamide and then again being essentially. pure alcohol than. Distillate is obtained, while a residue of formamide and alkyl formate remains. This residue can advantageously that withdrawn from the reaction column. Reaction mixture added , whereby the yield of formamide is increased.

The separation of the reaction mixture can be carried out according to suitable known methods. Vardampfungs- or dustillation methods are carried out., Z. B. by fzaktionierte Distillation: at ordinary pressure or under reduced pressure or evaporation in a thin layer on heated rollers, etc. The distillation can be continuous or be carried out discontinuously.

EXAMPLE An equimolecular amount of formamide and methyl alcohol is filled into a glass tube, 5 cm in diameter and 60 cm in length, which is cooled with water and filled with glass Raschig rings. Via flow meters, gaseous ammonia and methyl formate are simultaneously introduced below: into the column, whereby the temperature of the column is in the range. is held from io to 2o °. When the reaction is complete, flow. the Rcaktiomsprodukte from the top of the column continuously and turn collected. The results shown in the following table are achieved: Inflow-free analysis of the mixture obtained Time velocity molar ratio ammonia free 24 find after the reaction Grams per minute of ammonia in minutes methyl formate reaction immediately free methyl methyl Methyl to ammonia mixture according to the ammonia formamide alcohol formate formate ammonia ammonia o% *) reaction ° / a ° / o °%. ° / a Start 6.8 1.64 1, z2: 1 - 15 6.8 1.64 1, z2: 1 3.2 25 6.8 1.64 1.12: 1 3.9 0.01 53.4 38.1 8.5 30 6.8 1.64 i, 12: 1 - - 35 6.8 1.25 454: 1 - 50 6.8 1.25 1.54: 1 3.1 0.017 46.6 33.1 2 0, 3 55 6.8 1.25 1.54: 1 3.2 135 60 6.8 1.25 1.54: 1 -. *) These values were obtained from the mixture drawn off at the bottom of the reaction column at the time on which the main reaction took place. If the conditions of this example are changed to the extent that 6.8 g of methyl formate and 1.92 g of ammonia are introduced per minute, which corresponds to an equimolecular mixture of the starting materials, the product initially obtained contains 3.5% unreacted ammonia. After standing at room temperature for 24 hours, the composition of the product is as follows: Free ammonia. . . . . . . . . . o, 92% Formamide ... ... ........... 58, o 0/0 Methyladkohal. . . . . . . . . . . . . . 4I, 2 0/0 Methyl farmate. . . . . . . . . . . . . 0.0 0/0 I00, I 2 0/0 Instead of methyl formate, the z. B. by reaction of carbon monoxide with methyl alcohol, but also by esterification of formic acid: obtained with methyl alcohol. can be., Other alkyl formates or mixtures of. Alkylformia, th are used. To facilitate the complete separation of the farmamide from the alcohol, it is advisable to use an alkyl formate whose alcohol has a boiling point which is not too close to that of the formamide. In general, it is advantageous to use alkyl formates whose alcohols have relatively low boiling points in order to avoid temperatures during the distillation which cause decomposition or polymerization. The invention can also be applied in a manner other than that described in the examples, e.g. B. discontinuously, can be carried out in such a way that first the mixture of formamide and alcohol is added to the mixture of formamide and alcohol and only then gaseous ammonia is introduced into the mixture. The starting materials can also be fed to the reaction medium alternately. Furthermore, you can the ammonia with the alkyl formate before. Mix at the same time. Finally, the alkyl formate can also be added to the reaction mixture in vapor form.

Claims (2)

PATENT CLAIMS: i. Process for the production of. FoTmamid by reacting alkyl formate with anhydrous gaseous ammonia, characterized in that the starting materials are introduced into a mixture consisting of formamide and an aliphatic alcohol at normal pressure and temperatures below 6o °, preferably between 10 and 20 ° exists or contains these substances in addition to inert solvents. 2. The method according to claim i, through this. characterized, d.ass the reaction mixture after completion of the reaction let stand for a few hours. Attracted publications: German patent specifications. No. 658 188, 550 749, 6245o8.