DE2635280C2 - Process for the preparation of aliphatic monoisocyanates - Google Patents

Description

The invention relates to an improved process for the production of aliphatic monoisoeyanalcn from the corresponding carbamic acid chlorides.

Isocyanates are known to be produced by reacting amines with phosgene. The reaction proceeds via the stage of carbamide chloride c. the at higher "" temperature in the corresponding isocyanates and split hydrogen chloride. If the boiling point of the isocyanate to be produced is well above the decomposition temperature of carbamic acid chloride, the hydrogen chloride formed during the decomposition can in particular easily removed from the reaction chamber when using an inert organic solvent! However, if the decomposition temperature of carbamic acid chloride is close to above When the boiling point of the isocyanate lies, the isocyanate enters the gas space, where it joins the hydrogen chloride Carbamic acid chloride «combined. Therefore the split is imperfect; the isocyanate is only in low yield and contaminated with carbamic acid chloride obtain.

The described facts apply to aliphatic!. · Monoisocyanates, the aliphatic radicals of which contain 1 to 4 carbon atoms, with the difficulties are greatest in the production of methyl isocyanate.

Numerous procedures are described in the patent literature, which should eliminate the mentioned difficulties. Most of the procedures describe the split of carbamic acid chloride using hydrochloric acid.

So is known. Isocyanates from carbamic acid chlorides in the presence of organic bases (e.g. tertiary Amines) or carboxylic acid dialkylamides (DF.-OS 1593554) or TelraalkylharnstolTen (US-PS 3644461) to be produced in organic solvents. Furthermore, it is used to absorb the hydrogen chloride of water (DE-AS 21 56761) and of aqueous solutions or suspensions of inorganic bases (GB-PS 1208862). Olefins are also used as acceptors of hydrogen chloride called (DE-OS 22 10 285).

All the processes mentioned have the serious disadvantage that by-products are formed (corrosive organic or inorganic salts or alkyl chlorides), which either have to be processed costly or represent a negative environmental impact. In addition, there is the use of organic Bases the risk of side reactions to di- and trimeric Isocyanates. In the presence of water a considerable part of the carbamic acid chloride hydrolyzed to the amine hydrochloride, so that only in the case of the reactive

tertiary butyl isocyanate was found to be good yields will.

Also the production of low-boiling aliphatic monoisocyanates by thermal cleavage of Carbamic acid chlorides in organic solvents using special processing techniques are known.

According to DE-AS 1193034, the thermal cleavage of the carbamic acid chloride in a reactor equipped with a reflux cooler and a separating column carried out. Hydrogen chloride escapes through the reflux condenser, while isocyanate and carbamic acid chloride escape and solvents are retained. The isocyanate formed enters the column and can on The top of the column can be removed. Most of the isocyanate is returned through a return oil, damil rising hydrogen chloride in the column is completely absorbed and in the form of Carbamic acid chloride returned to the reactor. Hei to the continuous implementation of this process solution depleted in carbamic acid chloride is continuously removed from the Rciklor, elsewhere with Ciirbamidsäurcr.hlorid enriched and the reactor fed back.

In the German Offencnlegungsschrift 2411441, 2411442 and 2422211 process variants are described which are based on the principle specified in the above-mentioned process and which only concern changes in apparatus.
Although the processes mentioned enable the production of low-boiling aliphatic monoisocyanals by thermal cleavage of carbamic acid chlorides, serious disadvantages must also be mentioned here:

I. The removal of hydrogen chloride requires reflux condensers with large cooling surfaces that are operated with refrigerant in an energetically expensive manner must so that isocyanate and carbamic acid chloride are retained quantitatively.

2. For the separation of carbamic acid chloride by distillation Isocyanate from the reaction mixture, highly effective fractionation columns are required, whereby a high return ratio can be set got to.

3. The procedures can only be carried out cheaply, if relatively dilute carbamic acid chloride solutions (1 to 30%) can be used.

4. In the case of continuous implementation (on an industrial scale, only one is possible) the reaction solution must be led in a circle several times.

All of this has the consequence that the reaction components (Isocyanate, carbamic acid chloride and solvent) evaporated and condensed several times in the process, or have to be cooled down and reheated, which causes high energy consumption. the end the use of dilute solutions and the need for many circuits result in a long residence time and thus a low space-time yield. Due to the long dwell time there is a risk of a reduction in yield by trimerization of the monoisocyanate. The process requires a lot of measurement and Control technology. From this, from the low space-line yield and the need to use Highly effective fractionation columns result in a high investment outlay for technical production.

The present invention now opens up a completely new possibility, low-boiling aliphalic Monoisocyanates from the corresponding Carbaniidsäurechloridcn in good yields without major Apparatus expenditure to be produced, with a recombination of hydrogen chloride having to be approved monoisocyanate stay completely excluded !.

The new one on which the present invention is based The principle consists in the carbamic acid chlorides having at least one active hydrogen atom Reacting compounds with elimination of hydrogen chloride to form adducts of the desired monoisocyanates and then these adducts thermally into the desired monoisocyanate and the used as auxiliary, cleavage of at least one compound having an active hydrogen atom. Simultaneously with this Thermal cleavage of the adducts results in the distillative separation of the cleavage products.

In this way it is possible to make the carbamic acid chlorides the hydrogen chloride quantitatively and in pure form at low levels in a short time without the need for equipment Remove temperature from the reaction mixture, with the recombination of isocyanate and hydrogen chloride to carbamic acid chloride cannot occur, since the isocyanil is completely attached to that used Resources added. The C'arhaniidsäurechlurid-IVeic then cleaves Addition compound at a higher temperature again, and the released Isocyanai can be isolated quickly and in pure form by distillation without any problems.

The present invention thus provides a process for the preparation of aliphatic monoisocyanates the formula

R NCO
in which

R for an optionally olefinically unsaturated alinhiiiischcn Hydrochloride Tresl with 1 to 4 carbon atoms, from the corresponding carbamic acid chlorides the formula

R NH CO Cl

characterized in that the carbamic acid chlorides in the presence of under the reaction conditions inert solvents with at least one active hydrogen atom containing compounds under Splitting off of hydrogen chloride to form addition compounds the isocyanate R converts NCO and the addition compound is then thermally converted into the desired Isocyanate R-NCO and the compound having at least one active hydrogen atom decomposed, wherein at the same time the monoisocyanate formed is distilled from the at least one active hydrogen atom Disconnects.

Starting compounds for the process according to the invention are carbamic acid chlorides of the formula

R NH CO Cl
in which

R for an optionally olefinically unsaturated aliphatic hydrocarbon radical with 1-4 carbon atoms stands. In particular, R can represent a methyl, ethyl, n-propyl iso-propyl. n-butyl, iso-butyl-, sck-butyl-, terl-butyl-. or propenyl-K) Group standing. R 1 "Or is preferably a methyl group.

Such carbamic acid chlorides are formed by reacting the corresponding amines R NH ₂ with phosgene with elimination of hydrogen chloride. In the process according to the invention, the carbamic acid chlorides can also be used in a mixture with up to equimolar amounts of the corresponding monoisocyanates R — NCO. Such carbamic acid chloride-isocyanate mixtures are formed by partial thermal elimination of hydrogen chloride from the corresponding carbamic acid chloride.

In the process according to the invention, the carbamic acid chlorides or the carbamic acid chloride-isoeyanal mixtures are used preferably in 5 to 50 percent by weight solutions in under the reaction conditions inert organic solvents used.

The following solvents can be used, for example: Aliphatic hydrocarbons such as pentane. Hexane, Heptane, octane. Cyelohcrtan. halogenated aliphatic 5n hydrocarbons such as methylene chloride, chloroform. Carbon tetrachloride. n-propyl chloride. n-butyl chloride and isomers, amyl chloride. Cyclohexyl chloride, ethylidene chloride. Dichloroethylene. Ethylene chloride. Dichloropropane. Dichlorobulane. isopropyl bromide, n-propyl chromium «Mid. Butyl bromide. Ethyl iodide. Propyl iodide as well as fluorinated ones or partially fluorinated compounds; aromatic and substituted aromatic hydrocarbons like benzene. Toluene. Xylene, ethylbenzene. Chlorobenzene. Dichlorobenzene. Fluorobenzene. Difluorobenzene. Nitrobenbo zol, aromatic ether; Naphthalene derivatives such as chloronaphthulin: Ketones such as acetone, methyl ethyl ketone, diethyl ketone. Acetophenone: esters such as ethyl formate, alkyl acetate. Propionic acid ester. Phthalic acid esters and other high-boiling esters; otherwise organic compounds such as carbon disulfide. Methyl-tert-butyl-ether. Ethyl Propvlather. Tetrahydrofuran, Acetonitrile. Mixtures of the solvents mentioned can of course also be used

/earth. Preferably are chlorohenzene and / or Uhylene chloride used.

Min-Icstcns suitable for the method according to the invention Organic containing an active water solubility atom Connections are especially those that

t) have a ^{boiling point which is at least 20 c} C above the reflux temperature,

>) React in the temperature range from -20 to 100 ⁰ C with carbamic acid chlorides with ChlorwassersloiYabspaliung to isocyanate addition compounds and

:) their addition compounds with aliphatic monoisocyanates of the above form! R-NCO cleave the corresponding monoisocyanate in the temperature range from 100 ⁰ C to 250 ⁰ C.

In particular, those which are preferably suitable for the method according to the invention correspond to these prerequisites Connections which have at least one grouping of the Form!

-SO ₂ -NHR ₁

have, where R, stands for an aliphatic or aromatic hydrocarbon radical and preferably denotes a methyl, ethyl, propyl or bulyl group. In addition to the groups mentioned, these compounds have no further under the reaction>: conditions of the process according to the invention on. Particularly preferred compounds of this type are N-monosubstituted amides of sulfuric acid or of organic mono- or polysulfonic acids of the formulas

SO ₂ (NHR ₁ ) ,. R ₂ SO ₂ NHR ₁ . R _, (SO ₂ NHR,) ₂ .
In these latter formulas has

R _{1 has} the meaning already given above, while
R _{2 represents} an aliphatic hydrocarbon radical with 1-20, preferably 14, carbon atoms, a phenyl or a p-toluyl radical and
Rj stands for a phenylene or alkyl group with 1 3 carbon atoms.

Typical examples of these particularly preferred ones Connections are /.B. N.N'-dimethyl sulphurous acid diamide. N.N'-dibutyl-sehwcfclsäurediamid. ΝΑ ethyl-ethanesulfonic acid «mid. N-methylbenzenesulfonic acid amide, N-butyl-naphlhalinsulphonic acid amide. N.N'-Diethylbenzene-1,4-disulfonic acid diamide or N.N'-dipropylpropane-l.S-disulfonic acid diamide.

The at least one grouping of the formula which is suitable for the process according to the invention

-SO ₂ - NHR,

Compounds containing can in principle from the corresponding acid chlorides, i.e. sulfuryl chloride or the chlorides of organic sulfonic acids and primary amines with elimination of hydrogen chloride graze.

For methods according to the invention there are in addition to those which are preferred or particularly preferred Compounds also conversion products of sulfuryl chloride Iw organic sulfonic acid chlorides with primary Di- otler polyamines into consideration. For the production Auxiliaries suitable for the process according to the invention include, for example, the following sulfonic acid chlorides In question: Aliphalic sulphate chloride with I bis 20 carbon atoms like Melhansilfonsfiurechlorid.

Alhanesulfonic acid chloride, Hulansulfonic acid chloride, OK-tadecanesulfonic acid chloride, Methane disulfonic acid chloride or technical mixtures of various sulfonic acid chloride c as they occur in the sulfochlorination of aliphatic hydrocarbons (Ullmann, Vol. 16.

P. 562). Furthermore, aromatic sulfonic acid chlorides of benzene, toluene and naphthalene with 1 to 4 SO ₂ Cl groups are used. As examples are

called: benzenesulfonic acid chloride, p-toluenesulfonic acid chloride, Benzyl sulfonic acid chloride, benzene-1,3-disulfonic acid dichloride.

Examples of primary amines are: methylamine, Ethylamine, n-propylamine, iso-propylamine, butylamine, ethylenediamine, propylenediamine-1,2, propylenediamine-1,3. 1,4-diaminobutane, 1,6-diaminohoxane. Cyclohexyiamtn, aniline, inert substituents on the core comprising anilines.

The process according to the invention is generally carried out as follows:

In the temperature range from -20 to +100 ⁰ C, the reaction of the at least one active WasscrstolT alom-bearing compound effected mil Carbamidsäurcchlorid under the ChlorwasscrstolTabspaltung in the presence of the above-exemplified solvents. For this purpose, the reaction partners are preferably mixed at room temperature, the components being chosen so that at least one active hydrogen atom of the auxiliary is available per carbamic acid chloride group, preferably 1 1.5 hydrogen atoms of the auxiliary. After mixing of the starting materials, the reaction ie the set ACI duktbildung under elimination of hydrogen chloride by gentle heating within said temperature range preferably to 60 to 80 ⁰ C in motion. After at least 90% of the theoretically expected amount of hydrogen chloride has been split off and the reaction vessel has escaped, the second stage of the reaction according to the invention, the thermal cleavage of the addition product obtained, takes place. For this purpose, it is sufficient that Reaktionsgcfäß to a temperature within the temperature range of 100 25O ⁰ C, preferably at 130 to heat) ⁰ C to IM. The monoisocyanate formed distills off immediately after its formation. Depending on the boiling point of the solvent used, mixtures of

w monoisocyanal and solvent used are obtained as distillate, which have to be subjected to a further distillation for the purpose of further separation. When using low-boiling solvents, these dissolve before the decomposition temperature of the adduct is reached, while when using high-boiling solvents they remain in the reaction gel. In general, the major amount of produced this isocyanate at a cleavage temperature from 130 to 160 ⁰ C. In order to Vervollstündigung the cleavage is Vlie sump temperature to 160-250 ⁰ C, preferably about 200 ⁰ C. increased.

After the isocyanate has been separated off, the isocyanate used is present Auxiliaries in the sump unchanged from> ". By adding more carbamic acid chloride solution, the product can

b5 must be repeated several times, if this is intended, so the cleavage is expediently not completely completed in each case, in order to avoid unnecessary temperature stress to avoid the reaction components.

It can already be seen from the above explanations. that the method according to the invention is very suitable for continuous implementation. For this purpose, several reaction vessels are connected behind each other in a cascade, for example in Komi. Ciirbamidsäurechloridlösung and auxiliaries are continuously mixed unil the first Reaktionsgcfüü supplied in which the hydrogen chloride is split off at about 50 ° C to 70 ⁰ C of the main part. In the second reaction vessel, the dehydrochlorination is completed at 7O ⁰ C to 100 ⁰ C. In the third and possibly further reaction gel, the isocyanate is released and together with the solvent it is desiccated. The aid is returned to the starting point of the process from the bottom of the last reaction vessel. The isocyanal, the solvent which may also contain carbamic acid chloride, is isolated from the distillate or the combined distillates by fractionation

UlKlCiCl Siuüc i'nii C iiruiiiTiiuSiiürCCiiiOriii iitiULTCiCtlLT!

and fed back into the process.

The aliphatic monoisocyanates which can be prepared by the process according to the invention are valuable starting compounds for pesticides and pharmaceuticals.

example 1

In a 41 four-necked flask with a stirrer, contact thermometer and packed column (height = 30 cm. diameter 5 cm) with back divider closes at 20.degree 1026 g (6MoI) benzenesulfonic acid c-niethylamide a Solution of 467.5 g (5 mol) of N-methylearbamic acid chloride given in 500 ml of chlorobenzene. In the course of 1 hour the temperature is increased to 100 ° C., whereby 98% of the calculated amount of hydrogen chloride with the reflux divider through the column and the closed the attached reflux condenser escape and be absorbed in water. Then there is a mixture the reflux temperature of the chlorobenzene (130 C) is heated. At this temperature, the methyl isocyanate begins to be split off. which for another 3 hours by gradually increasing the vaccination temperature at 200'C and with the return divider open, escapes together with the chlorobenzene. A mixture distills from 276 g (4.84 mol) of methyl isocyanate. 5 g of N-methylcarbamic acid chloride and 540 g of chlorobenzene. (Crude yield 97%). When redistilling this mixture 270 g (4.74 mol) of pure, chlorine-free methyl isocyanate are obtained (pure yield 94.7%).

Example 2

In the apparatus described in Example 1 are 654 g (6 mol) methanesulfonic acid methylamide with 467.5 a (5 mol) N-methyl carbamic acid chloride in 5 (M) ml of chlorobenzene mixed at 20 ° C. By gradual The temperature increase to KM) C will be 97% of the calculated chlorine water length within 90 minutes cleaved.

It is then gradually heated to 1.V) -C. Hey At this temperature, methyl isocyanate begins to distill off together with the solvent. Taking gradually Temperature increase distill between 130 ° C and 200'C within 4 hours together with the Solvent from 270.8 g of methylene isocyanate (corresponding to 95% of theory). The net yield according to the Re

distillation amounts to 267.9 g of methyl isocyanate (corresponding to 94% of theory).

Example 3

Analogously to Example 1, 620 g (5 mol) of N.N'-dimethylsulftirylamide are found with 537.5g (5MoI) N-ethylcarbamic acid chloride implemented in 500 ml of o-dichlorobenzene. It will be after cleavage of the adduct and redistillation of the isocyanal solvent mixture 319.5 g of ethyl isocyanate (corresponding to 90% of theory).

Example 4

Analogously to Example I, 73Xg (6 mol) of methanesulphonic acid ethylamide are used with 607.5 g (5 mol) of N-isopropyl carbamic acid chloride implemented in 500ml chlorobenzene. the

2 »Theory.

Example 5

As in Example I, UlOg (6MoI) p-toluene

^2% sulfonic acid methylamide reacted with 607.5 g (5 mol) of N-propylcarbamic acid chloride in 500 ml of xylene. The pure yield of n-propyl isoeyanate is 96% of theory.

Example 6

In the apparatus described in Example I are reacted with 467.5g (5MoI) N-Methylearbamidsüurechlorid in 500ml of chlorobenzene to 100 ⁰ C 12X2.5 g (7.5MoI) Benzolsulfonsüure-methylamide. The temperature is then increased to 160 ° C. within 30 minutes and held at this level for a further 3 hours

4 (i 3 (X) ml of chlorobenzene dropwise added. Ks is distilled in an isocyanate solution millel gas away. which contains 3.5 mol of methyl isocyanal (corresponding to 70% of theory). After the sump has cooled, 327.3 g (3.5 mol) of N-methylcarhanide acid chloride are obtained in l'orm of 50% chlorobenzene solution added and. as described in Melhylisocyanai transferred. The process is repeated four more times, each time the one obtained Methyl isocyanate equivalent amount of N-methylcarbamic acid chloride replace.! will. The results are listed in the following table:

Slack 55 1 ! -. insalz Methyl isocyanate im 2 Mole Carhiimid- Distillate (in moles) 3 sulfur chloride M, 4 5 3.5 5 3.5 3.4 6th 3.4 3.6 3.6 3.3 3.3 3.4 3.4 3.2

A total of 2075.7g (22.2 mol) N-methylcarbh5 amide acid chloride used. When redistilling the combined Deslillalc are 1145.7 g (20.1 mol) of Methyüsocyanal (corresponding to 90.5% of theory) won.

Claims (2)

Patent claims: 1. Process for the preparation of aliphatic Monoisocyanates of the formula R NCO.
in which R for an optionally olefinically unsaturated aliphatic KOhlenwasserslofTresl with 1 4 Carbon atoms, from the corresponding carbamic acid chloride of the formula R-NH-CO Cl. characterized in that the carbamic acid chlorides in the presence of solvents which are inert under the reaction conditions with at least an active wassersloiTalom containing compounds with elimination of hydrogen chloride Addition compounds of the isocyanates R NCO converts and the addition compound is then thermally converted into the desired isocyanate R NCO and having at least one active hydrogen alom Compound decomposed, at the same time the monoisocyanate formed dcsiillaliv from the at least separates a compound having an active hydrogen atom .; 2. The method according to claim!. Characterized in that that as at least one active hydrogen ~ .lom containing compounds the characteristic grouping - SUN, NHR ₁ containing amides of sulfuric acid or organic sulfonic acids are used, where R _{1 is} an aliphatic hydrocarbon.