JPS59106448A - Production of isocyanate - Google Patents

Abstract

PURPOSE:To prepare an isocyanate useful as a raw material of polyurethane, in high rate of reaction and high yield, suppressing the by-production of high- boiling substance, by thermally decomposing a carbamic acid ester in the presence of a quaternary ammonium salt as a catalyst. CONSTITUTION:A carbamic acid ester is thermally decomposed in the presence of a quaternary ammonium salt (e.g. tetramethyl ammonium chloride, decylbenzyl trimethyl ammonium chloride, etc.) as a catalyst, at 200-500 deg.C, preferably 250-400 deg.C under normal pressure -0.1mm.Hg. The produced isocyanate and alcohol are taken out of the system in the form of vapor, and condensed and separated to obtain the objective compound. The amount of the catalyst is 0.01- 10wt%, preferably 0.1-5wt%, based on the weight of the carbamic acid ester.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing incyanates by heating and thermally decomposing carbamate esters (hereinafter referred to as urethanes) together with a catalyst.

More specifically, the present invention provides a method for producing corresponding incyanates by thermally decomposing urethanes, which comprises thermally decomposing the urethanes in the presence of a quaternary ammonium salt as a catalyst. Concerning a method for producing cyanates.

Isocyanates are practically extremely useful substances mainly as raw materials for polyurethane, and tolylene diisocyanate, methylene bis-(4-phenylisocyanate) tolylene diisocyanate, and the like are currently produced commercially on a human scale.

The current manufacturing method for these isocyanates, taking fle as an example, is to first nitrate toluene to dinitrotoluene, then reduce this with hydrogen to form diamine, and then use phoscene to produce diisocyanate. It consists of a complicated process that involves handling large amounts of highly toxic phosgene and producing hydrogen chloride as a by-product. Therefore, instead of this method, a simpler and cheaper manufacturing method without using phoscene has been desired for a long time, and although various studies have been carried out, it has not yet been realized.

One method that can replace the current method for producing isocyanates using the phosgene method is a method for producing isocyanes-1 by thermally decomposing urethanes.

However, conventionally known thermal decomposition methods have problems such as isocyanate yield, reaction rate, equipment material, temperature control, by-product removal, etc.
: However, there are disadvantages that make it difficult to implement industrially, and it is economically disadvantageous, so it has not been put to practical use as a production method for INCYANE-1. As a result of intensive research into these problems, the inventors of the present invention have found that the above two drawbacks can be solved by catalytically decomposing urethanes using a specific catalyst, and have thus come to provide the present invention.

The reaction for producing inocyanates by thermal decomposition of urethanes is shown by the basic formula (1).

■7Nf(Co2R'→RNC○+R'CI-I
(Ll However, when the urethane thermally dissociates, several undesired side reactions usually occur at the same time, such as the formation of secondary amines, or the decarboxylation of the urethane with the by-products of primary amines R, NH2, and olefins. Reactions are known, such as reactions between produced isocyanates and raw urethane with the by-production of allophanates, reaction between produced isocyanates and by-product amines with the by-production of urea compounds, and polymerization of produced isocyanates.

Further, the thermal dissociation reaction of formula (1) is a reversible reaction, and dissociation occurs upon heating, and the reaction shifts to the right side. This thermal dissociation temperature varies depending on the type of urethane and reaction conditions.

Therefore, in order to advantageously obtain incyanates from urethane, it is important to suppress the side reactions and dissociation reactions mentioned above and selectively perform the thermal decomposition of formula (1) to obtain iso-anates. .

Conventionally, thermal decomposition of urethanes is roughly divided into two methods: a method in which the thermal decomposition is carried out at a high temperature in the gas phase, and a method in which the thermal decomposition is carried out at a relatively low temperature in the liquid phase.

As the former method, there is a method of thermally decomposing urethane under reduced pressure and at a temperature of 350 to 550 DEG C. while keeping the residence time to within 5 seconds (Japanese Patent Application Laid-Open No. 50-117745). However, even with this method, solid polymer is produced as a by-product and accumulates in the reaction tower during long-term reactions, making continuous operation difficult and causing great difficulty in putting this method into practical use.

As the latter method, a method has been proposed in which urethanes are diluted with an inert bath medium and thermally decomposed at a relatively low temperature of about 175 to 350 DEG C. (Japanese Patent Laid-Open No. 50-30832). By adopting these methods, the yield of isocyanate may be improved, but it is still not sufficient, and especially when producing polyvalent isocyanates such as obtaining diisonoanate by thermal decomposition of diurethane. However, the problem of high boiling point by-products still remains.

The present inventor has investigated various methods for producing isocyanate by suppressing side reactions and improving the yield in a method for producing isocyanate by thermally decomposing urethane. It was found that the thermal decomposition reaction was accelerated and the yield of isocyanate was increased.

The method of the present invention includes, for example, thermally decomposing urethanes by contacting them with a catalyst, preferably at normal pressure or lower pressure and at a temperature of 200 to 500°C, in the presence or absence of an inert solvent, and producing isocarbons. In this example, the amphoteric acid and the alcohol (alcohol or phenol) are taken out as vapor, and the amphoteric acid is separately condensed and collected. In this case, incyanate urethane, which is partially dissociated from the urethane groups of the polyvalent urethane, may be produced in the middle, but the vapor produced by the reaction is immediately fractionated and the high-boiling components are refluxed to the reactor. Alternatively, by condensing all produced vapors other than alcohol components, distilling the target isocyanate from one isocyanate fraction, and circulating the bottoms to the reactor, the intermediate point between the two high points can be obtained. A method is adopted in which the isocyanate is converted into the desired polyvalent isocyanate.

The urethanes used as raw materials in the present invention are represented by adducts of inocyanates and alcohols or phenols, and the urethanes used in the method of the present invention are monovalent, divalent, or trivalent aliphatic, Expressed as a combination of aromatic, cycloaliphatic or aliphatic isocyanyl-1-valent to -valent to tetravalent aliphatic, aromatic, aliphatic, alcohol or phenol. It is a thing, kohj) is Sara(
(Has a substituent or incyanate group that does not react with the incyanate group such as a halokene atom, nitro group, cyano group, alkyl group, alkoxy group, acyl group, alkoxy group, ether group, thio-ether group, carbonyl group, etc.) You can leave it there.

JA, weight 1 is methyl carbanilate, ethyl carbanilate, propyl carbanilate, butyl carbanilate, '\quinle carbanilate, octyl carbanilate, ethylene dicarbanilate, fluoropylene carbanilate-1- 1l-limethylene dicarbanilate, -\xamethylene dicarba = L/-), ri) ceryltricarbanylate, pentaerythrylte) lacarbanilate, ethyl-p-phenylcarbanilate, methyl-p-methyl Carbanilate, ethyl-p-chlorocarbanilate, ethyl-3,4-dichlorocarbani L/-
), Methyl-3,4-dichlorocarbanilate, Impropyl-m-chlorocarbanilate, Ethyl-2-methyl-5-ditrocarbanilate, Ethyl-4-methyl-
3-incyanatocarbanilate, methylene bis-(4
-ethylcarbanylate-1-), methylene his-(4-methyl carbanilate), diethylphenylene-1,3-
7carbame]l-, diethylphenylene-], 4-7carbamate, diethylnaphthylene-J, 5-dicarbamate, dimethyltos/cycarbamate, diethyltridine dicarbamate, C2-ethylhexyltrisine dicarbamate , diethyl dianisidine dicarbamate, ethyl isoporone dicarbamate, methylene his-(4-ethyl chlorohexyl carbamate), dimethyltolylene-2,4-dicarbamate, diethyltolylene-2,4-dicarbamate, dimethyltrilene Ren-2
, 6-dicarbamate t-, diethyl 1. IJshi7-2
．． 6-Cicalhame-1, diisopropyltolylene-
2,4-dicarbamate, diisopropyltolylene-2
, 6-dicarbamate, dibutyl!・Rylene-2,4-
Dicarbamate, di-2-ethylhexyltolylene-2
, 4-dicarbamate, dinocrosoxyltolylene-
2,4-dicarbamate, diphenyltolylene-2,4
-Dicarbamate, di(ethoxyethyl)tosolene-2
．． 4-dicarbamate, diethyl-4-chlorophenylene-1,3-dicarbamate, triethylbenzentriyl], 3.5-1-IJ carbamate, etc. are available.

Examples of quaternary ammonium salts that can be used in the method of the present invention include those of the general formula (AI, A2 is an alkyl or alkenyl group having 1 to 18 carbon atoms, A3. A, t41 to 18
an alkyl group or alkenyl group having 6 carbon atoms, or a benzyl group, an alkylpencyl group, an aryl group,
Alkylaryl group or halogen, cyano group, 21
・Represents a pencil group or an aryl group substituted with an alkoxy group. X represents a halogen such as CI, Br, I, etc. ), and one of the quaternary ammorum salts is the compound represented by the general formula "%O@a, xO".
Quaternary pyridinium salts can also be used, where R
1 represents an alkyl group, an alkenyl group, a pencil group, or an alkylbenzyl group having 1 to 24 carbon atoms, R represents hydrogen, an alkyl group, a cyano group, an acyl group, and X represents CI, Represents Haloken such as 13r and I.

Specifically, tetramethylammonium chloride, tetraethylammonium tallolite, tetrapropylammonium furomite, tetrabutylammonium iodide, trioctylmethylammonium chloride, n-decyltrimethylammonium tallolide, lauryltrimethylammonium chloride, cetyltrimethylammonium chloride. , stearyltrimethylammonium chlorite, distearyldimethylammonium chlorite, pennortrimethylammonium cuchlorite, todesolpencil trimethylammonium chlorite, laurylbenzyltrimethylammonium chloride, /methyldenorpencylammonium bromite, occudenyl dimethylpencil ammonium chloride, dodeso/l/cy) -5-/l/3.4-dichloropentylammonium chloride, dimethylphenylbennolammonium chloride, 3-methoxyphenoxyethylethylpensylammonium chloride)
"Equivalent force; fi ') Pyrinnium salts include laurylpyridinium chloride, cetylpyridinium chloride, hexadenrubiricinium bromide, stearyl-α-picolinium bromide, cetyloxomethylpyri/niumtalolite, stearamide, methylpyrinonium Examples include chloride, 2-dodecyl inquinolinium bromide, and the like.

The quaternary ammonium salt compound preferably has a weight ratio of 0.01 to 10% relative to the weight of the urethane.
1 to 5% by weight is used.

In thermally decomposing urethanes by the method of the present invention, the reaction temperature is usually 200°C to 500°C, particularly 250°C.
Celsius to 400°C is preferred. Further, the pressure is selected to be such that the produced isocyanates can be vaporized at the above reaction temperature. A: Usually carried out at a pressure of normal pressure to 0.1 mmHg.

Urethanes are thermally decomposed to produce incyanates, alnials, or T4 phenols, which can be used efficiently.The incyanates and alcohols or phenols become vapor and can be used for transportation in some cases. Take it out of the reaction system by transporting it with an inert gas. The mixed vapor taken out of the system is condensed and separated into isocyanate and alcohol or phenol due to the difference in condensation temperature between the two fractions.

As stated above, if urethane is thermally decomposed according to the method of the present invention, it is possible to obtain isocyanate in good yield by suppressing the by-product of high-boiling substances at a high reaction rate.

EXAMPLES The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples unless it goes beyond the gist.

Example 1 A pyrolysis reactor was prepared by filling a glass tube with a diameter of 6 cm and a length of 50 cm with a stainless steel Raschig ring, and heating the tube to 300° C. from the outside. Nitrogen gas is supplied to the reactor at 72 m/min.
One sink at a ratio of 0 ml. In addition, in order to separately condense the isocyanate and alcohol gases that come out of the rice after decomposition, there is a water-cooled trap followed by an acetone-dry ice cooling trap.

2.4-7 ethyltrilenosycarbamate was fed into the reactor at a rate of 209-7 ethyltrilenosycarbamate per stone of free volume of the reactor per minute. In addition, denpensyltrimethylammonium chloride was supplied as a catalyst in an amount of 1% based on the weight of dicarbamate. Then, the gas that comes out from the decomposition is separated and condensed. At this time, the isocyanate fraction 13. As a result of analysis by sy/ro, the target tolylene 2,4-diisocyanu-1- (hereinafter abbreviated as 2.4-TDi) was found.
662% by weight and the amount of intermediate tolylene-2-isocyanate and tolylene-4-isocyanate-2-power.2. The yield of 4-TDi was 683% of the raw material dicarbamate.

Comparative example 1.

In this comparative example, thermal decomposition was carried out in the same manner as in the example without using a catalyst.

An incyanate fraction of 12.097 minutes was obtained. As a result of gas chromatography analysis, objective 2. 4-TDiba51
,, 51j mass %, the intermediate tolylene-2-ylananate-4-carbamate is 251 wt %, same < tril)
Syn-4-insyanate-2-carbamate is 153
% by weight.

As a result, 2. The yield of 4-TDi was 472% based on the raw material dicarbamate. From this result, thermal decomposition is considerably slow, there are many intermediates, and non-distillates are increasing. That is, the catalyst selectively promotes the thermal decomposition of urethane,
It is clear that the effect of suppressing side reactions is significant.

Example 2 Using the same apparatus as in Example 1 above, the temperature of the decomposition reactor was maintained at 4.00'C, and 30 g of 2,4-diethyltolylene difluoride-1 was added per minute to the reactor. Supply it. Further, cetylpyridinium chloride was added as a catalyst at a ratio of 0.15% by weight based on 7 carbamates. The produced isocyanate fraction was transferred to Casta OC at 19.69/min.
As a result of the analysis, 948% by weight of the target 2.4-TDi and the intermediate tolylene-2-inocyanate were found.
173% by weight of 4-carbamate, 115% by weight of tolylene-4-isocyanato-2-carbamate, and by-product tolylene-4-amino-2-isocyanate 094
Weight + A- was maintained.

From this, the yield of 2.4-'I'Di was 947% by weight.

Repeat the same exercise as in Example 2 except that no catalyst is added.
child. The produced isocyanate fraction was 931/min, and the results of cassloscopic analysis showed that 2.4-TDi was 90.2% by weight, the intermediate tolylene-2-isocyanato-1-rubamate was 326% by weight, and tolylene-4-isocyanato -2-carbamate or 2.44% heavy H% by-product tolylene-4-
Amino-2-isocyanate is 41% by weight. From it, 2.4. - Yield of T4 to 1! ? 887
It was %. This result will be implemented! Compared to Ill 2, when the number of bites is 4, the amount of intermediate monoisocyanate is large, so the reaction rate is slow, and the by-product tolylene-4-amino-2
-The amount of isocyanate has increased four times. The instant catalyst is
It has a remarkable effect of promoting thermal decomposition of carbamate and suppressing side reactions.

Example 3 Using the same equipment as in Example 1 above, the decomposition reactor temperature was set to 25
CVC was maintained at 0°C, and diethyl tridine dicarbamate was fed into the reactor at a rate of 15 so/min. Further, as a catalyst, dodenlepenciltrinotyl ammonium chloride was added in an amount of 13% by weight based on the dicarbamate. The distilled inocyanate fraction is collected in a water-cooled condenser and
I got my share.

Gas chromatography analysis of the residue revealed that it was 971% by weight of tolyne diisozoanate (hereinafter abbreviated as TODi).
and the intermediate toridine monoisocyanate monokore T
The yield of ODi was 981%.

Comparative Example 3 The same procedure as in Example 1 was repeated except that no catalyst was added.
In fact, the isocyanate fraction is 11. The result of gas chromatography analysis was 874% by weight of ODi and 33% by weight of monoisocyanate.

From this, the yield of TODi was 90%.

Example 4 Using the same equipment as in Example 1, the temperature of the decomposition reactor was increased to 3.
It was kept at 50'C. diethyl) in this reactor
l) supplying syndicarbamate at a rate of 201/min;
child. In addition, as a catalyst, tetramethylammonium chloride was added at a ratio of 0.25% by weight to dicarbame-1 (c).The distilled incyanate fraction was collected in a water-cooled condenser to obtain 14.9 mm/min. Results of analysis by gas chromatography: TODi 9 9.5% by weight, monoisocyanate 0
It was 5% by weight.

From this, the yield of TODi was 996%.

Comparative Example 4 The same operation as in Example 4 was carried out except for adding a catalyst. The inocyanate fraction was obtained at 14.89-/min.
The composition was 3.4% by weight of TODi 9 and 45% by weight of monoisocyanate. From this, the 'FODi yield was 932%.

Example 5 Using the same equipment as in Example 1 with the decomposition reactor temperature maintained at 300'C, di-2-ethyl\quinlutridine cicalhamate was fed at a rate of 3077 minutes.

As a catalyst, ben/rutrimethylammonium B90ride was added in an amount of 0.1% to the raw material. The decomposed isocyanate fraction was collected in an air-cooled receiver to obtain 1517 fractions. Gas chromatography analysis of Koga T (]5
50 weight 'FODi'.

From this, the yield of 'J'ODi was 94%.If catalyst 2 was not added, the yield of 'I'ODi was 83%.

Example 6 Using the same equipment as in Example 6 in which the temperature of the decomposition reactor was kept at 300°C, diethyl tridine dicarbamate was treated with 25P.
It was fed at a rate of 1 minute.

Collect 18. IP/min was obtained. Analysis by gas chromatography showed that the TODi was 98.0% by weight and the monoisocyanate content was 15% by weight. From this, the yield of 'l'ODi is 955%
On the left. When the same operation was performed except that no catalyst was added, the ODi yield was 895%.

Patent applicant: Nippon Kayaku Co., Ltd. 404-

Claims (1)

[Claims] A method for producing incyanate H, which comprises thermally decomposing carbamates in the presence of a quaternary ammonium salt as a catalyst.