DE2705695A1 - METHOD FOR PRODUCING ALKYLISOCYANATES - Google Patents

Description

BAS? Corporation

Our reference: O.Z. 32 433 H / cl 67ΟΟ Ludwigshafen, February 9th, 1977

Process for the preparation of alkyl isocyanates

The invention relates to a process for the preparation of alkyl isocyanates by dehydrohalogenation of the corresponding Carbamic acid halides by reaction with isocyanates whose boiling point is above the decomposition point of the corresponding carbamic acid halides lies.

It is known that isocyanates can be prepared by phosgenating primary amines and then phosgenating the carbic acid chlorides formed thermally dehydrochlorinated. However, this synthetic route is for lower alkyl isocyanates whose boiling points are above Decomposition temperatures of the corresponding carbamic acid chlorides are unsuitable, since the overheated isocyanate is reached when it is reached the decomposition temperature of the carbamic acid chloride in the vapor space and at the colder parts of the apparatus with hydrogen chloride in an exothermic reaction to form carbamic acid chloride would recombine.

For production of lower alkyl isocyanates of the dehydrochlorination in the presence Carbaminsäurechloride is therefore recommended to perform inorganic or organic bases (US-PS 2 i "80088; DT-PS 1 233 85 ^1"; DT-PS 1,668,109). Inorganic bases are added in the form of aqueous solutions so that the reaction takes place in a two-phase reaction medium. This leads to side reactions, for example the formation of urea or hydrochlorides, which reduce the isocyanate yield. In addition, expensive drying of the organic phase and the work-up of saline wastewater are necessary. When using organic bases, hydrochloride precipitates are produced, the regeneration of which causes difficulties, especially when the system is operated continuously.

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From DT-PS 1 193 03 ** a method is known according to which Alky! .Isocyanates, the boiling point of which is below the decomposition point of the corresponding carbamic acid chlorides, by thermal decomposition of the corresponding carbamic acid chlorides in Presence of an organic solvent can be obtained. The resulting hydrogen chloride is passed through a reflux condenser removed from the reaction chamber, while the alkyl isocyanate is distilled off at the same time via a separately arranged column.

To obtain carbamic acid chloride-free isocyanates, you must very low space-time yields are accepted. Inevitably, the carbamoyl chlorides and isocyanates are thus used exposed to high thermal stress, which is the cause of the increased occurrence of by-products, e.g. trialkylcyanuric acid, Allophany! Chloride, is.

A process for the production of alkyl isocyanates has been established of formula I.

R-NCO I,

in which R is unbranched or branched alkyl having 1 to 5 carbon atoms means, found, which is characterized in that a carbamic acid halide of the formula II

R-NH-CO-X II,

in which R has the meaning given above and X is halogen, by reaction with an isocyanate whose boiling point is above the decomposition point of the corresponding carbamic acid halide, dehydrohalogenated and the resulting alkyl isocyanate Formula I removed from the reaction space.

Advantages of the process according to the invention are the high yield and the excellent purity of the end product, the short reaction time and its technically easy feasibility. Due to the absence of auxiliary bases, the procedure is

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much more environmentally friendly than known processes. The only by-product obtained is pure hydrogen halide, for example can be further processed into hydrochloric acid.

The following reaction equation outlines the course of the reaction:

R-NH-CX + R'-NCO * R-NCO + R'-NH-CX

η η

0 0

II

Starting materials of the formula II or end products of the formula I are carbamic acid halides, in particular carbamic acid chlorides, or isocyanates, in the formula of which R stands for unbranched or branched alkyl having 1 to 5 carbon atoms and thus denotes the methyl, ethyl, propyl, butyl or pentyl radical.

The carbamic acid chlorides preferably used as starting materials are expediently prepared by gas phase phosgenation of the corresponding amines according to JACS 7.2, 1888 (1950).

Isocyanates whose boiling point is above the decomposition point of the corresponding carbamic acid chlorides are suitable for taking up the hydrogen halide released. High-boiling aliphatic or aromatic isocyanates, in particular aliphatic isocyanates, or mixtures thereof, come into consideration. It is expedient to use N-alkyl isocyanates with unbranched or branched alkyl radicals with 5 to 20 carbon atoms, for example amyl isocyanate, n-octyl isocyanate, dodecyl isocyanate, octadecyl isocyanate, 3 _f 5-dimethylhexyl isocyanate, decyl isocyanate, tetradecyl isocyanate, N-alkoxyalkyl isocyanates with 6 to 12 carbon atoms, for example in the alkoxyalkyl isocyanate 1-methyl-2-propoxyethyl isocyanate, propyoxypropyl isocyanate, isobutyloxypropyl isocyanate, cyclohexyloxypropyl isocyanate, N-cycloalkyl isocyanates with 6 to 12 carbon atoms in the cycloalkyl radical, e.g. cyclohexyl isocyanate, ß-decalyl isocyanate, alkyl diisocyanates with up to 12 carbon atoms

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atoms in the alkyl radical, e.g. tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, cycloaliphatic diisocyanates, e.g. ! »,!» '- dicyclohexylmethane diisocyanate, N-aryl isocyanates, e.g. Phenyl isocyanate, 1-naphthyl isocyanate, p-tolyl isocyanate, benzyl isocyanate, N-aryl isocyanate, e.g. 1,5-naphthyl diisocyanate. In addition, residues containing isocyanate groups, for example from phosgenation batches, can also be used.

The preparation of these isocyanates is known (Kirk-Othmer, Encyclopedia of Chemical Technology 1 £, 53-55 (1967); Ullmanns Encyclopedia of Industrial Chemistry, £, 1 ff (1957); Houben-Weyl, Methods of Organic Chemistry, £, 119 ff (1952)). After their production, they can be used without further purification.

The method according to the invention is expediently as follows carried out:

The equimolar amount of carbamic acid halide of the formula II is stirred into the high-boiling isocyanate; the resulting alkyl isocyanate of the formula I is then drawn off at a temperature below the decomposition temperature of the resulting carbamic acid halide and under reduced pressure. Accordingly, the volatility of the alkyl isocyanate of the formula I is advantageously a temperature range of -10 ⁰ C to +80 ⁰ C and a pressure range of 0.1 to 760 Torr.

Likewise, the resulting alkyl isocyanate by blowing in a Inert gas stream are expelled into the reaction mixture at normal pressure.

The reaction can also be carried out in the presence of an inert organic solvent. Aliphatic ones come into consideration Hydrocarbons, e.g. octane, ligroin, petroleum ether, chlorinated aliphatic hydrocarbons, e.g. 1,2-dichloropropane, 1,2-dichloroethane, cyclohexyl chloride, amyl chloride, cyclic hydrocarbons, e.g. cyclohexane, methylcyclohexane, decalin, tetrahydronaphthalene, aromatic hydrocarbons, e.g. benzene,

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Toluene, xylene, cumene, diethylbenzene, ethylbenzene, ethylnaphthalene, chlorinated aromatic hydrocarbons, e.g. monochlorobenzene, dichlorobenzene, chlorotoluenes, chloronaphthalenes, as well as Mixtures of these aliphatic and aromatic hydrocarbons, ketones, e.g. methyl ethyl ketone, acetophenone, esters, e.g. Ethyl acetate, butyl acetate, alkyl propionate with 1 to 4 carbon atoms in the alkyl radical, dimethyl phthalate, Phthalic acid diethyl ester, phthalic acid methyl ethyl ester. Aromatic hydrocarbons are particularly suitable and chlorinated aromatic hydrocarbons.

The process according to the invention can be continuous or discontinuous be performed.

The remaining carbamic acid halide of the high-boiling isocyanate can at a temperature in the range from 80 to 250 ° C, preferably 80 to 180 ° C, thermally dehydrohalogenated will. Last residues still remaining in the reaction solution of the alkylcarbamoyl chloride of the formula II are distilled off and recovered. The loss of substance, especially with continuous operation is extremely low.

Thermal dehydrohalogenation of the carbamic acid halide can be advantageous and thus the recovery of the high-boiling isocyanate by operating at reduced pressure or by introducing it be supported by inert gas or phosgene.

In those cases where the carbamic acid halide formed during the reaction is present in solid form, this can be achieved in solution by an excess of isocyanate or by adding a solvent being held.

The yields of alkyl isocyanate are in all cases over 85 % in the case of a discontinuous procedure and over 95% of theory in a continuous procedure. Th .. The last residues of the carbamic acid halide of the formula II which have not yet been converted into alkyl isocyanate are recovered in the thermolysis of the reaction residue and reused. The overall yield of implementation,

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based on the carbamic acid chloride of the formula II is quantitative. The alkyl isocyanates have a degree of purity of at least 97 % .

The isocyanates which can be produced by the process of the invention are valuable starting materials for the production of crop protection agents, Pesticides, dyes, synthetic resins and plastics, textile waterproofing agents, Detergents, bleaches and adhesives. In particular, their conversions to urethanes, e.g. for use as Foams or high molecular weight coatings with high flexibility, or ureas are important. Regarding the use is based on the aforementioned publications and Ullmann's Encyclopedia der technical chemistry, volume 9, pages 11, 12, 404 (1957) and volume 17, page 204 (1966).

example 1

46.7 parts by weight of methyl carbamic acid chloride are introduced into 125 parts by weight of cyclohexyl isocyanate at room temperature. The reaction mixture is now ^{heated to 40 °} C., methyl isocyanate is drawn off at a pressure of 100 torr and collected in a cold trap.
Yield: 87 % of theory; Bp. 38 ⁰ C.

Example 2

46.7 parts by weight of methyl carbamic acid chloride are stirred into 168 parts by weight of hexamethylene diisocyanate at room temperature. The reaction mixture is heated to 40 ° C., methyl isocyanate is stripped off at a pressure of 100 torr and collected in a cold trap.
Yield: 89% b.p. d.Th.j 38 ⁰ C..

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Example 3

54 parts by weight of ethylene carbamic acid chloride are introduced into 168 parts by weight of hexamethylene diisocyanate at room temperature. The reaction mixture is heated to 30 to 35 ⁰ C, at a pressure of 75 Torr Äthylenisocyanat is withdrawn and collected in a cold trap.
Yield: 90 % of theory; Bp 60 ° C.

Example 4

121.5 parts by weight of isopropylcarbamic acid chloride are introduced into 84 parts by weight of hexamethylene diisocyanate at room temperature. The reaction mixture is heated to 40 ° C; at a pressure of 50 torr, isopropyl isocyanate is drawn off and collected in a cold trap.
Yield: 92 % of theory; Bp 74/75 ° C

Example 5

60.8 parts by weight of isopropylcarbamic acid chloride are dissolved in 168 parts by weight of hexamethylene diisocyanate at room temperature. At an internal temperature of 50 ^° C. and a pressure of 50 torr, the isopropyl isocyanate formed is collected in a cold trap.
Yield: 90 % of theory; Bp 73/74 ° C.

Example 6

In 126 parts by weight of hexamethylene diisocyanate, dissolved in parts by weight of chlorobenzene, 121.5 parts by weight of isopropylcarbamic acid chloride are introduced at room temperature. The reaction mixture is heated to 50 ° C; at a pressure of Torr, isopropyl isocyanate is drawn off via a column and collected in a cold trap.
Yield: 85 % of theory; Bp 73/75 ° C

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Claims (5)

Claims 1./Process for the preparation of alkyl isocyanates of the formula I R-NCO I, in the R unbranched or branched alkyl rait I bis 5 carbon atoms means characterized in that a carbamic acid halide of the formula II R-NH-CO-X II, in which R has the abovementioned meaning and X is halogen stands, by reaction with an isocyanate whose boiling point is above the decomposition point of the corresponding carbamic acid halide is dehydrohalogenated and the resulting alkyl isocyanate of the formula I removed from the reaction chamber. 2. The method according to claim 1, characterized daft, is dehydrohalogenated the carbamic acid halide of the formula II at a temperature in the range of -10 to +80 ⁰ C under a pressure of 0.1 to 760 Torr. 3. The method according to claim 1, characterized in that the reaction is carried out in the presence of an inert organic solvent. 4. The method according to claim 1, characterized in that the alkyl isocyanate of the formula I is removed from the reaction space with the aid of a stream of inert gas under normal pressure. 5. The method according to claim 1, characterized in that the carbamic acid halide formed in the dehydrohalogenation of the carbamic acid halide of the formula II after removing the alkyl isocyanate of the formula I from the reaction 809833/0184 - 9 - ORIGINAL INSPECTED . '«\'; \ J» i ™ ■! ■ "lif'Pr ''!!!!!];! ¹¹¹ ™ ¹¹ '!!' ¹¹ '' ¹ - "" I ¹ '' · ■ tr- o.ζ. 32 433 room at temperatures in the range of 80 to 25O ° C thermally dehydrohalogenated and the isocyanate formed again used for the dehydrohalogenation of the carbamic acid halide of the formula II. BASF Aktiengesellschaft 809833/0184