FR2520359A1 - PROCESS FOR THE PRODUCTION OF ISOCYANATES FROM ESTERS OF AROMATIC CARBAMIC ACIDS - Google Patents

Abstract

THE INVENTION CONCERNS THE PRODUCTION OF ISOCYANATES FROM AROMATIC CARBAMIC ACID ESTERS (URETHANS). THE PROCESS CONSISTS OF CONVERTING AROMATIC CARBAMATES INTO THEIR CORRESPONDING ISOCYANATES BY THERMOLYSIS AT A PRESSURE AT LEAST EQUAL TO ATMOSPHERIC PRESSURE IN THE PRESENCE OF A CATALYST CHOSEN BETWEEN TI, SN, SB AND ZR. APPLICATION TO THE PRODUCTION OF POLYMERIC AROMATIC CARBAMATES AND ISOCYANATES FROM ALKYL AROMATIC COMPOUNDS.

Description

2520 G 9

  The present invention provides methods for converting aromatic carbamates and polymeric aromatic carbamates to their corresponding isocyanates by thermolysis in the presence of a specially defined catalyst at pressures equal to or greater than atmospheric pressure. Isocyanates are very useful substances

  as raw materials for polyurethanes These poly-

  Urethanes can be used in the formation of various products ranging from motor vehicle parts to thermal insulation products. The properties of the final polyurethane product are determined to a large extent by the number of isocyanate groups,

  that is, -NCO, present on the starting isocyanate.

  For example, difunctional isocyanates do not produce crosslinking and are useful in the production of

  flexible polyurethane foams Polyester isocyanates

  functional groups result in crosslinking and are therefore

  useful for the production of rigid polyurethane foams.

  In the class of polyfunctional isocyanates is a subclass of isocyanates, namely polymeric aromatic polyisocyanates which have gained a reputation in the market and which have remarkable properties which make them particularly suitable for special end applications such as the production of polyisocyanates. The term "polymeric isocyanates" as used herein refers to a mixture of compounds containing polyalkylene oligomers or the like.

  -arylene-polyarylisocyanates such as polymethylene

  polyphenyl isocyanate (hereinafter described in more detail). Non-polymeric aromatic isocyanates include compounds such as diisocyanato-toluene,

  methylene-bis- (4-phenylisocyanate) and diiso- vanato-naphthalene.

  A conventional process for the production of these

  non-polymeric isocyanates, for example diisocyanato

  toluene of formula: ONCO C t-NCO NCO o NCO

(I) (II)

  It consists in nitrating toluene to form dinitrotoluene, reducing it to hydrogen to form the corresponding diamine, then reacting the diamine with phosgene. Therefore, the process described above involves complicated and inconvenient steps, requiring use of a large quantity of highly toxic phosgene and allowing the formation of hydrogen chloride

as a by-product.

  Another method of preparing non-polymeric isocyanates involves the synthesis of carbamates from nitro compounds and the subsequent pyrolysis of carbamates to form isocyanate and an alcohol as a co-product. The reaction of isocyanate formation by pyrolysis of carbamates can be illustrated by the following basic equation:

RHNCO 2 R 'y RNCO + R'-OH (1).

  By thermal dissociation of carbamate, several

  unwanted side reactions take place at the same time.

  These side reactions are: the decarboxyline reaction

  carbamate dilution accompanying the formation of an RNH 2 primary amine and an RNHR olefin or secondary amine as a by-product; the reaction between the product isocyanate and the starting carbamate, allowing the formation of an allophanate as a by-product; the reaction between

  the isocyanate produced and an amine formed as

  product, allowing the formation of a urea compound as a by-product; and the polymerization of the isocyanate product allowing the formation of an isocyanurate or a by-product polymer The thermal dissociation reaction of equation (1) above is reversible and its equilibrium remains with the carbamate of the member left at low temperature but moves to the right by heating, so that dissociation of carbamate

  In this case, the temperature, thermal dissociation

  varies according to the type of carbamate and the conditions

  Therefore, to obtain isocyanates advantageously from carbamates,

  it is important to conduct the pyrolysis reaction of the equa-

  (1) selectively while inhibiting the reactions

  secondary and reverse mentioned above.

  The probability of occurrence of certain undesirable side reactions is increased as the reaction temperature is high and the period during which the isocyanate product remains in contact with the components of the reaction mixture increases. lowers the reaction temperature, the rate of reaction decreases, together with the solubility of the carbamate in any solvent used

in the reaction mixture.

  Conventional carbamate pyrolysis can be roughly classified in high temperature vapor phase reactions and relatively low temperature liquid phase reactions. U.S. Patent No. 3,734,941 discloses a typical vapor phase process. wherein a carbamate is pyrolyzed at 400-600 C in the presence of an acid

  of Lewis and the resulting vapor is divided by condensa-

  fractionation into an isocyanate and a

  In this process, for example, diisocyanato

  toluene in a yield of 60% by pyrolysis of tolylene

  2,4-diethyl dicarbamate of formula: CH 3

HCOOC 2 H 5 (III)

NHCOOC 2 H 5

  However, this process has the disadvantages of low product yield, catalyst decomposition, high temperature reaction apparatus corrosion and considerable amount of a polymer as a by-product (see also the specification of the

British Patent No. 1,247,451).

  German Patent No. 2,410,505 proposes as an improved process in the vapor phase a process in which the contact time of the

  Reaction bodies at 350-550 ° C are limited to 15 seconds.

  According to this process, the isocyanate yield reaches 93%, although the carbamate has been introduced

  in the form of powders in the reaction zone Any-

  time, a solid polymer is also formed as a sub-

  produced by this process and is gradually deposited in the reactor and the condenser during a sustained operation, which makes it difficult to conduct a continuous reaction.

  heat required for the endothermic pyrolytic reaction

  This additional factor has the effect that this process has great difficulty in being able to be supplied to the starting material in a very short period of time.

adopted in practice.

  Liquid phase processes have been studied to lower the reaction temperature and reduce

  unwanted side reactions.

  For example, the patent of the United States of America

  No 2 409 712 discloses the pyrolysis of carbonic esters

  substituted on the nitrogen atom in the liquid phase,

  in the presence or absence of a diluent, at temperatures

  150 to 3500 C under high vacuum to distill over the resulting isocyanate None of the carbamate esters

  disclosed does not include polymeric aromatic carbamates.

  As a result, not only the use of a vacuum

  pushed up the cost price of the process, but the use

  In the case of its application to the distillation of polymeric isocyanates, a high vacuum would be ineffective because of the very high boiling points of the latter. This patent does not disclose the use of catalysts either. of the type described

in this memo.

  In an article in the Journal of the

  American Chemical Society, volume 81, pages 2138 and following

  (1959), Dyer et al. show that ethyl carbanilate yields phenyl isocvanate (60-75 mol% based on degraded carbanilate) and ethyl alcohol when heated for 6 hours.

  hours at 200 C under sufficiently low pressure (3-

  16 k Pa) to vaporize the alcohol but high enough to retain the isocyanate At atmospheric pressure, no phenyl isocyanate is obtained, although 70% of the ethyl carbanilate is destroyed at 250 ° C. and at room temperature.

  atmospheric pressure, alpha-methyl carbanilate

  benzyl yields dominant amounts of aniline, alpha-

  methylbenzylaniline, styrene and carbon dioxide.

  U.S. Patent No. 3,054,819 discloses the pyrolysis of an aliphatic mornocarbamate and dicarbamic esters in the optional presence of a basic catalyst such as an alkali or alkaline metal oxide, hydroxide or carbonate. earthy, etc. Pyrolysis is conducted at pressures greater than the pressure

  atmospheric and at temperatures of 100 to 300 C.

  According to this process, the isocyanate obtained as

  must be separated from the glycol ester formed as a co-product, preferably by distillation of the isocl-nate alone or together with the glycol ester and separating.

  neither of these variants is available.

  in the case of polymeric aromatic isocyanates.

  Therefore, this patent does not disclose (1) the use of

  aromatic carbamates of any type

  nor (2) the use of the catalysts of the present invention

  together with all carbamates.

  U.S. Patent No. 3,919,278 is directed to a process for the preparation of isocyanates, wherein a mononuclear aromatic carbamate is dissolved in an inert solvent at a rate selected such that the total concentration of carbamate and a product obtained by pyrolysis of this carbamate is in a range of about 1 to 20 mole%, and pyrolysis of the carbamate is conducted at 230-200 C in the presence of an inert carrier used in an amount of at least three molar proportions relative to the carbamate Polymeric aromatic carbamates are not mentioned in this patent not

  more than is the use of the catalysts of the pre-

  this invention together with all carbamates.

  U.S. Patent No. 3,919,279 relates to a process for producing isocyanates in which a carbamate is dissolved in an inert solvent and the

  solution is brought into contact at high temperature (ie

  ie 175-350 C) with a catalyst consisting of a heavy metal (Mo, V, Mn, Fe, Co, Cr, Cu or Ni) or a compound of this metal to carry out the pyrolysis of the carbamate at temperatures of 175 to 350 ° C. The concentration of the carbamate dissolved in the inert solvent is less than 80% by weight, for example between about 3 and about 1% by weight, 3% representing the lower limit of solubility of the carbamate in the solvent. emphasis on the importance of maintaining the carbamate in a state almost completely dissolved at the reaction temperature during conversion to the isocyanate to minimize the formation of polymerization products such as tars or resins as well as unwanted products The alcohol product is removed from the reaction mixture at atmospheric pressure or at a pressure greater than atmospheric pressure in the examples given. This patent does not disclose the catalysts described. in this memoir nor the thermolysis of

  polymeric aromatic carbamates.

  U.S. Patent No. 3,962,302 is directed to a process for producing isocyanates by thermolysis of carbamates dissolved in an inert organic solvent and in the absence of a catalyst.

  reaction temperatures range from 175 to 350 C (preferably

  200 to 300 ° C.) at carbamate concentrations of 3 to 80% by weight of the reaction solution. This patent does not disclose the thermolysis of polymeric aromatic carbamates or the use of catalysts.

  of the present invention with all carbamates.

  U.S. Patent No. 4,081,472 relates to a process for the production of aromatic isocyanates by thermolysis of an aromatic carbamate at temperatures of 150 to 350 ° C (preferably 200 to 300 ° C) at a pressure below atmospheric pressure in the presence of a catalyst dissolved in an inert solvent The resulting isocyanate and alcohol should be removed as vapor during the reaction and then condensed separately (see column 5, lines 55 and following and column 9, line 27 et seq.) Accordingly, the process must be carried out at a pressure below atmospheric pressure. Suitable catalysts include

  compounds of Cu, Zn, Al, Sn, Ti, V, Fe, Co and Ni.

  Although it is recommended to dissolve the carbamate in a solvent, the process can be carried out with the carbamate in the form of suspension or emulsion (column 8, lines 20 et seq.). This patent does not disclose the thermolysis of polymeric aromatic carbamates and thermolysis of aromatic carbamates at pressures equal to or greater than atmospheric pressure; U.S. Patent No. 4,146,727 discloses a process for producing dicarbamates and

  polymeric carbamates In this patent, it is

  dre (see column 1, lines 25 and following and column 4, lines 56 and following) that the polymeric carbamates described therein can be thermally decomposed

  in a solvent to their corresponding polymeric isocyanates

  in accordance with two of the above-mentioned patents

  United States Patent Nos. 3,919,279 and 3,962,302, despite the absence of details in these two patents as indicated above or in the aforementioned Patent No. 4,146,727, which concerns the

way to get this result.

  U.S. Patent No. 4,163,019

  discloses a process for producing 4,4'-alkylidene

  diphenyldiisocyanate according to a procedure comprising

  two stages, involving the condensation of a phenylalkyl-

  carbamate using an aldehyde or a ketone to form a dimer, for example a dicarbamate, and an exchange reaction in which a phenyl isocyanate

  is mixed with the dicarbamate to form a phenyl

  alkylcarbamate and the corresponding diisocyanate Some tin compounds are revealed as catalysts

  This reference does not make any reference to

  Use of these catalysts for the thermolytic cracking of carbamates in the absence of an exchange reaction. An article in Chemical Week, November 9, 1977, pages 57-58 discloses a process comprising steps of reacting nitrobenzene,

  carbon monoxide and an alcohol to form urethra

  corresponding thannes (alkylphenylcarbamates) The reaction product is reacted with formaldehyde to

  produce a condensate that contains a p, p'-methylene-

  Diphenyldialkylcarbamate and higher oligomers This product is, in turn, thermally decomposed into the corresponding "polymeric diisocyanates" and into alcohol which is recycled. The reaction conditions mentioned involve the use of high temperatures in the range of 100 to 200 ° C. in the reaction zone. first reaction stage and from 200 to 300 C in the decomposition stage, and the

  reaction leads to a mixture of polymeric diisocyanates.

  This article does not disclose the use of the catalysts described herein for purposes of the present invention. There are several difficulties in attempting to conduct the thermolysis of polymeric aromatic carbamates. These polymeric materials are much less soluble in customary solvents than non-polymeric materials. As a result, even slight side reactions such as occur between an isocyanate and a carbamate reduce the solubility of the polymeric reaction product much more than would be expected from similar reactions in which nonpolymeric reactants are used. Once the polymeric material begins to solubilize,

  the formation of tars, gums and other sub-

  undesirable products begin to accelerate Low reaction temperatures also reduce the rate of the decomposition reaction, requiring longer reaction times Longer reaction times may promote the occurrence of undesirable side reactions, although at lower speed If the reaction temperature is high to increase the reaction rate and the solubility of the polymeric reactants and / or products and by-products, other

  unwanted side reactions begin to

  fest at an accelerated pace, at these high temperatures.

  In addition, if the concentration of the polymeric carbamate is too high in solution, the polymeric isocyanate product (which is not volatile under the reaction conditions and can not be removed economically from the reaction medium by vaporization) reacts more quickly with the polymeric carbamate to form an allophanate that is even more insoluble than the polymeric reactants or the isocyanate obtained as

  produced, thus destroying the reaction sequence.

  Dilution of the reactants with a solvent reduces the cost effectiveness of the process and requires a greater

  investment of capital in the equipment of the

tion.

  Consequently, an enuilibre must be established between the reaction temperature and the concentration and the solubility of the polymeric carbamate to allow the economic implementation of the process. It is for this reason and for those which are explained above that has continually investigated ways to reduce the decomposition reaction temperature of polymeric carbamates without limiting the reaction rate to any degree of significance or, as a

  Alternatively, to increase the speed of reaction to temperatures

  similar conditions used in the absence of a catalyst.

  A reduction of the reaction temperature would attenuate the undesirable side reactions caused by higher temperatures. The increase in the reaction rate leaves less time for undesirable side reactions to take place until the moment of reaction.

the separation of the product.

  With respect to non-polymeric aromatic carbamates, the prior art described above clearly indicates that conventional reaction temperatures disclosed for thermolysis of carbamates to form the corresponding isocyanates range from about 175 to 3500 C at equal pressures. or higher than the atmospheric pressure As a result, we also

  continuously seeking ways to lower the temperatures

  pyrolytic pyrolysis of non-polymeric aromatic carbamates

  below 1750 C in order to reduce unwanted condensation reactions which occur at high temperatures and consequently increase selectivity.

  to the isocyanate, or alternatively, to

  increase the rate of decomposition reaction of car-

  non-polymeric aromatic bamates at conventional pyrolysis temperatures to reduce the average residence time of the reactants in a reactor so as to allow a reduction of the capital invested in the equipment (for example by reducing the dimensions

reactor).

  The development of the present invention results

  research mentioned above.

  According to one of its aspects, the present invention proposes a process for the production of at least one isocyanate

  aromatic from at least one aromatic carbamate.

  These carbamates are described herein and include polymeric aromatic carbamates as well as non-polymeric aromatic carbamates. This process involves heating a mixture or solution of at least one of said carbamates in the presence of a metal-containing catalyst. said metal being selected from the group consisting of Ti, Sn, Sb, Zr and mixtures thereof, under conditions and in a manner sufficient to convert said carbamate to at least one isocyanate, and at least one alcohol, said heating being conducted to a pressure at least equal to the atmospheric pressure; to separate said alcohol from said isocyanate and to collect

the isocyanate of the solution.

  In accordance with the present invention,

  aromatics are thermally decomposed into their corresponding isocyanates and alcohol in the presence of

at least one catalyst.

  The aromatic carbamates used in the present invention can be classified into two categories:

  aromatic non-polymeric carbamates and carbamates

polymeric aromatic mates.

  The non-polymeric aromatic carbamates (i.e. carbamic acid esters) which can be used in the process of the present invention are represented by the formula: R 1 + NHCOOR 2) n (IV) in which R 1 is a monovalent, divalent or trivalent (preferably monovalent or divalent) aromatic hydrocarbyl group normally containing from about 6 to about 32 (e.g. 6 to 22), preferably about 6 to about 18 (e.g. in particular about 6 to about (for example 6) carbon atoms R 1 may carry an isocyanato group or a monovalent or divalent substituent unreactive toward an isocyanato group R 2, in the formula IV, is selected from monovalent hydrocarbyl groups, saturated aliphatic saturated or aromatic alicyclic acids normally having not more than 10 (for example 8) carbon atoms, preferably not more than 6 carbon atoms and not more than 4 (for example 2) carbon atoms, and R 2 may carryan isocyanato group or a monovalent substituent not reactive towards an isocyanato group Similarly, in the formula IV, N is a number having a representative value of 1 to 3, preferably 1 or 2 and in particular 1, and corresponds to the

valence of group R 1.

  Examples illustrating the substituent R 1 are aryl groups such as phenyl, tolyl, xylyl, naphthyl, biphenylyl, anthryl, phenanthryl, terphenyl, naphthalenyl, pentacenyl and methylenebiphenyl and the like.

  divalent or trivalent groups formed by removing

  respectively one or two hydrogen atoms to these aromatic groups These aromatic groups may carry an isocyanato group; a substituent unreactive to this group, such as an alkyl group, normally a C 1 to C 5 alkyl group, a halogen atom, a nitro group, a cyano group, an alkoxy group having, for example, 1 to 5 carbon atoms, carbon, an acyl group, an acyloxy group or an acylamido group; or a divalent substituent of a similar nature, such as a methylene group, an ether group, a thioether group, a carbonyl group or a

carboxyl group.

  Examples illustrating the substituent R 2 include aliphatic groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl and methoxyethyl and alicyclic groups such as

than a cyclohexyl group.

  Representative examples of carbamates that

  can be used in the present invention including

  Methyl N-phenylcarbamate, ethyl phenylcarbamate, propylphenylcarbamate, phenylcarbamate

  butyl, octyl phenylcarbamate, naphthyl-1-

  ethyl carbamate, ethyl anthryl-1-carbamate,

  ethyl 9-anthryl-carbamate, anthrylene-9,10-

  diethyl dicarbamate, ethyl p-biphenylcarbamate,

  diethyl m-phenylenedicarbamate, naphthylene

  Diethyl 1,5-dicarbamate, methyl p-tolylcarbamate, ethyl ptrifluoromethylphenylcarbamate,

  isopropyl m-chlorophenylcarbamate, 2-methyl-5-

  ethyl nitrophenylcarbamate, 4-methyl-3-nitrophenyl-

  ethyl carbamate, 4-methyl-3-isocyanatophenyl

  ethyl carbamate, methylene-bis- (phenyl-4-methyl)

  carbamate), dimethyl tolylene-2,4-dicarbamate,

  diethyl tolylene-2,4-dicarbamate, 2,6-tolylene

  diethyl dicarbamate, diisopropyl tolylene-2,4-dicarbamate, dibutyl tolylene-2,4-dicarbamate,

  diphenyl tolylene-2,4-dicarbamate, tolylene-

  Diphenyl 2,6-dicarbamate, di (ethoxyethyl) tolylene-2,4-dicarbamate, diethyl 4-chlorophenylene-1,3-dicarbamate, methyl pbutoxyphenylcarbamate, ethyl p-acetylphenylcarbamate, and the like. ethyl nitrophenylcarbamate, isopropyl m-trifluoromethylphenylcarbamate and trimethyl N-phenyltricarbamate. Among these carbamates, the most practical examples are tolylenedicarbamates, naphthylenedicarbamates,

  methylene-bis- (phenylcarbamates) and mixtures thereof.

  The polymeric aromatic carbamates which can be used in the process of the present invention comprise a mixture of carbamates, the components of said mixture being represented by the formula: (X) 4 (Ar> R - + Ar 'R Ar' Mnf (V )

n I -

  Wherein X represents a monovalent group -NHCO 2 R 2, R 2 having the definition given with respect to formula IV above; R 1 is independently selected from (a) a divalent saturated straight or branched chain aliphatic group having, for example, from about 1 to about 10, preferably from about 1 to about 5, and especially about 1 to about 2 carbon atoms, (b ) a divalent saturated alicyclic group having, for example, from about 4 to about 10, preferably from about 5 to about 8 and in particular from about 6 to about 8 carbon atoms, and (c) a divalent aromatic group having, for example

  about 6 to about 18, preferably about 6 to about

  14 and in particular about 6 to about 10 carbon atoms; n is a number from about 1 to about 4, preferably from about 1 to about 3 and especially about 1 or about 2 (eg 1); Ar is a substituted or unsubstituted aromatic hydrocarbyl group, for example an aromatic hydrocarbyl group having 6 to 14, preferably 6 to 10 and especially 6 carbon atoms, excluding substituents, said substituents being selected from halogens (c); that is F, Cl, Br and I), the group -NH 2 and mixtures thereof; and n "is a number which can vary from 0 to about 5 or more on any individual carbamate of the mixture, and the average numerical value of n" for all the carbamates of the mixture

  ranging from about 2.0 to about 3.5, for example,

  from about 2.2 to about 3.0 and in particular about

  2.5 to about 2.8 All polyaromatic aromatic carbamates

  mentioned above are considered as

conventional in the prior art. Representative examples of groups R 2 and R 3 suitable in the

  Associated Formula V in a single carbamate include the following:

R 2 R 3

  Methyl Methylene Methyl Dimethyl Methyl Trimethylene Methyl Methyl Ethyl Methyl Ethyl Methyl 2,2-Dimethyl Trimethylene Methyl 2 Methyl Trimethylene Methyl 1,3 Cyclopentylene Methyl 1,4 Cyclohexylene Methyl 1,4-Phenylene Ethyl Methylene Ethyl Dimethylene Ethyl 2,2 Dimethyl Trimethylene Isopropyl Methyl Iso- propyl Trimethylene isopropyl 1,4-phenylene cyclopentyl methylene phenyl methylene The most preferred R 2 group is methyl, since it forms an alcoholic co-product

  having the lowest boiling point.

  The most preferred polymeric aromatic carbamate is a mixture of poly-N-lower alkyl,

  Example C 1 to C 4) -polymethylenepolyphenylcarbamates.

  In formula V, the identity of the substituents carried by the aromatic hydrocarbyl group may be influenced to be a halogen, in an effective manner to impart flame retardant properties to the final polyurethane to which the isocyanate derived from the In addition, some of these substituents of the formula V may be residual -NH 2 groups which depend on the process, and which are left by the process,

  used to prepare the polymeric carbamate.

  Processes for the preparation of aromatic carbamates

  non-polymeric materials are well known in the art

  earlier and do not require further comment.

  The preparation of polymeric aromatic carbamates can be conducted in accordance with US Patents

  No. 4,146,727, No. 4,172,948 and No. 4,202,986.

  The catalyst which is used to facilitate the thermolysis reaction comprises at least one metal, preferably used in the form of at least one compound

  polar material containing this metal, preferably an organic compound

  polar, said metal being selected from the group consisting of Ti, Sn, Sb, Zr and mixtures thereof.

  homogeneous reactions, these metal compounds are pre-

  Preferably, the non-metallic portion of said catalytic compound preferably has at least one polar functional group sufficient to solubilize. in the liquid carbamate (i.e. the non-solvent form) and / or the solvent (i.e., the solvent form), a catalytic amount of metal as hereinafter defined. although the preferred method for solubilizing the metal catalyst is the use of a polar organic metal compound, other methods for solubilizing the catalyst in an inert solvent can be used. Within the scope of the organic metal compounds are metal salts formed with

  aliphatic, alicyclic and aromatic carboxylic acids

  such as formic acid, acetic acid, lauric acid, stearic acid, oxalic acid,

  azelaic acid, naphthenic acid, tetrahydro-

  phthalic acid, benzoic acid, phthalic acid and pyromellitic acid; metal alkoxides formed with aliphatic and alicyclic alcohols such as methanol, ethanol, propanol, butanol, octanol, dodecyl alcohol,

  benzyl alcohol, ethylene glycol, propylene glycol, poly-

  ethylene glycol, glycerol, pentaerythritol and cycloalcohol

  hexyl chloride and the metal trialkoxides

  respondents; metal phenolates formed with monohydroxylic or polyhydric phenolic derivatives

  such as phenol, cresol, nonylphenol, catechol and hydro-

  quinone as well as the corresponding metal thiophenolates

  respondents; metal salts of sulfonic acids such as methanesulfonic acid, ethanesulfonic acid, dodecanesulfonic acid, cyclohexanesulfonic acid, benzenesulfonic acid, toluenesulfonic acid and dodecylbenzenesulfonic acid; metal chelates formed with chelators, for example beta-diketones such as acetylacetone and benzoylacetone, keto esters such as ethyl acetylacetate and ethyl benzoate; metal carbamates formed with the carbamates defined as starting material for the present invention as well as the corresponding metal thiocarbamates and dithiocarbamates, metal salts of compounds bearing anionic ligands such as the nitric acid group, the phosphoric acid group, the acid group boric and cyanato group; and complexes

  metallic salts of the various metal salts mentioned

  above with ligands having a pair of electrons without covalent like amines, phosphines,

  phosphites, nitriles and amides.

  Representative examples of suitable catalysts

  include zirconium tetra-2,4-pentanedionate

  nium, tributoxy-antimony, tetrabutoxytitanium, tetrapropoxy zirconium, tetraoctyloxytitanium

and their mixtures.

  A popular class of catalysts includes the

  tin catalysts These tin compounds are pre-

  of organic tin compounds represented by the following formula: (R 4) 4a Sn (B) (VI)

  wherein R 4 is a hydrocarbyl group selected inde-

  between alkyl groups, normally alkyl groups having from about 1 to about 18, preferably about 1 to about 10, and most preferably about 1 to about 5 carbon atoms, and aryl groups having, for example, about 6 to about 14, preferably 6 carbon atoms; B is independently selected from the group consisting of halogen (i.e., F, Cl, Br, I), preferably Cl, alkoxy (i.e., -OR), e.g. alkoxy having from about 1 to about 8, preferably about 1 to about 6 and especially about 1 to about 4 carbon atoms; an alkancyloxy group (i.e. O-CCR), for example an alkanovloxy group having from about 1 to about 8, preferably from about 1 to about 6 and especially from about 1 to about 4 carbon atoms, an oxo group and a hydroxy group; and "a" is an integer of 1 to 3 The group (R 4) is preferably an alkyl group to promote catalyst volatility when

the desire.

  Representative examples of catalysts

  suitable tin represented by formula VI

  butyl-Sn (O) OH, dipropyldimethoxytin,

  dibutyloxotin, tributylmethoxytin, triphenyl-

  hydroxytin, trichloromethyltin, dibutyl dimethoxy

  Tin, trimethylhydroxytin, dichlorodiethyltin, trimethylchloretin, triphenylethanoyloxytin, diphenyldichlorotin, and mixtures thereof. It is also possible to use halogenated inorganic tin compounds such as tin tetrachloride and tin dichloride.

  Preferred catalysts include butyl

  Sn (O) OH, dibutyloxotin, tributylmethoxytin, triphenylhydroxytin, trichloromethyltin,

  dibutyldimethoxytin, tributylmethoxytin, tetra-

  tin chloride and mixtures thereof

  Metal compounds for which ineffective catalytic activity has been observed include tetraethyltin (characterized by its lack of polar functional group), dichlorotriphenyl antimony (characterized by the + 5 valence state of antimony) and 2,4-dichlorodi-4. Titanium pentanedionate (characterized by extreme steric hindrance around the metal portion represented by titanium) As a result,

* in choosing a suitable catalyst, one must first

  avoid the characteristics just mentioned to obtain a catalyst endowed with an effective activity. It has been found that the catalysts described herein, including tin catalysts,

  significantly accelerated the thermal decomposition

  aromatic carbamates and their corresponding alcohols

  to a degree of transformation of about 90%.

  This is extremely beneficial in offering the choice between conducting the reaction below conventional pyrolysis temperatures and conducting it at conventional temperatures but with obtaining the product at a much higher rate, thereby reducing reactor size. necessary to produce quantities

  similar isocyanates obtained in accordance with the

  Another advantage of the present invention is that the process using the catalysts defined above is carried out at atmospheric pressure (i.e. at an absolute pressure of 0.098 M Pa) or at pressures above atmospheric pressure (e.g., absolute pressures of 0.098 to 1.4 M Pa). The use of atmospheric pressure permits the use of more advantageous solvents which have relatively low boiling points. and that would otherwise be collected with the product at subatmospheric pressure, which would require additional separation operations. It also eliminates the need to use

  expensive apparatus operating under vacuum.

  The process of the present invention is carried out in the liquid phase by heating the carbamate, preferably a carbamate solution, in the presence of the catalyst described above. If no solvent is used, the carbamate must be liquid state during the thermolysis reaction It is provided by choosing the reaction temperature above the melting point of the carbamate. In order to dissolve the carbamate, an inert organic solvent is preferably used. Any solvent which is temperature-stable can be used. of the reaction, i.e. a solvent which does not decompose or react with any of the reactants, which can solubilize the carbamate at the reaction temperature and has a boiling point which exceeds, preferably at least 250 C, the reaction temperature

at the reaction pressure.

  Thus, the inert organic solvent acts by dissolving the carbamate as well as the resulting isocyanate

  at the reaction temperature and, where appropriate, in

  catalyst and other potential by-products.

  The inert organic solvent also acts by uniformly dispersing heat throughout the reaction mixture, and by diluting carbamate and reaction products

  to such an extent that the undesirable side reactions

  The solvent will preferably dissolve the catalyst, although the catalyst may be used in a heterogeneous state, for example

  example in a form fixed on a support.

  Suitable inert organic solvents

  take hydrocarbons, ethers, thioethers ketones, thioketones, sulfones, esters, organosilanes, halogenated aromatic compounds and mixtures thereof

  Representative examples of suitable solvents

  include chlorobenzene, o-dichlorobenzene;

  Diethylene glycol dimethyl ether, dimethyl ether,

  triethylene glycol, the dimethyl ether of the tetra-

  ethylene glycol (also called tetraglyme), 1,6-

  dichloronaphthalene, methoxynaphthalene; hydrocarbons

  aliphatic bures such as higher alkanes, dodecane, hexadecane, octadecane and liquid paraffin; the corresponding alkenes; petroleum fractions of the paraffin series such as are commonly used as lubricating oils or cutting oils; alicyclic hydrocarbons such as petroleum fractions of the naphthene series; aromatic hydrocarbons such as dodecylbenzene, dibutylbenzene, methylnaphthalene, phenylnaphthalene, benzylnaphthalene, biphenyl, diphenylmethane, terphenyl and aromatic petroleum fractions usually used as rubber processing oils; and substituted aromatic compounds

  no reactivity with isocyanate, such as chloro-

  naphthalene, nitrobiphenyl and cyanonaphthalene; ethers and thioethers such as diphenyl ether, methylnaphthyl ether, diphenyl thioether, and similar aromatic ethers and thio ethers; ketones and thioketones such as benzophenone,

  phenyltolylketone, phenylbenzylketone, phenylnaphthyl-

  ketone and similar aromatic ketones or thioketones; sulfones such as diphenylsulfone, etc., aromatic sulfones; esters such as animal and vegetable oils, dibutyl phthalate, dioctyl phthalate, phenyl benzoate and similar aromatic and aliphatic esters; organosilanes such raw

  conventional silicone oils and mixtures thereof.

  Preferred solvents include hexadecane, chlorobenzene, o-dichlorobenzene, diethylene glycol dimethyl ether, dimethyl ether, and the like.

  triethylene glycol, the dimethyl ether of the tetra-

  ethylene glycol, dichloronaphthalene, methoxynaphthalene

and their mixtures.

  Although any amount of effective solvent can be used to perform the described functions

  above, these effective quantities represent ordinary

  from about 50 to about 98, preferably from about 50 to about 90 and in particular from about 50 to about 80

  weight, based on the total weight of the solvent plus carbamate.

  The amount of catalyst that is present during the reaction, preferably dissolved in the solvent, is any amount effective to accelerate the pyrolysis reaction in relation to the uncatalyzed reaction. Thus, although any effective amount can be used of catalyst, these effective amounts normally constitute from about 0.001 to about 0.3 moles, preferably from about 0.01 to about 0.2 moles and especially from about 0.01 to about 0.1 moles of catalyst metal, per mole.

  of carbamic ester group carried by the carbamate.

  Pyrolysis of non-polyaromatic aromatic carbamates

  is conducted at temperatures ranging from

  at about 200 C (for example 80 to 200 C) and

  from about 80 to about 150 C (e.g.

at 125 C).

  Pyrolysis of polymeric aromatic carbanates is conducted at a temperature of about 30 to about 300 C, preferably about 80 to about 250 C (e.g.

  at 180 ° C.) and in particular from about 80 to about 1500 ° C.

  It is crucial for the present invention that the pressure at which the pyrolysis reaction is conducted for polymeric aromatic carbamates or

  non-polymeric is at least equal to the atmospheric pressure

  It is also possible to use higher pressures

at atmospheric pressure.

  The reaction time for carbol pyrolysis

  non-polymeric aromatic mate-

  the particular temperature chosen, the reaction temperature used

  However, the reaction time is shortened by the catalyst of the present invention with respect to the reaction time when no other catalyst is used. catalyst under similar reaction conditions, up to a conversion rate of about%. As a result, for discontinuous reactions

  conducted under the reaction conditions defined below.

  above, the reaction times normally vary from about 1 to about 120 minutes, preferably from about 1 to about 60 minutes and especially from about 1 to about 15 minutes.

  minutes for non-polymeric aromatic isocyanates.

  Reaction times under conditions similar to those indicated above for reactions

  with polyisocyanate aromatic isocyanates

  The amounts normally vary from about 0.1 to about 120 minutes, preferably from about 0.5 to about 60 minutes.

  and in particular from about 1 to about 15 minutes.

  Reaction times for a continuous process vary depending on the carbamate concentration at various stages during the reaction sequence <e.g.

  if multiple reactions are used).

  As indicated above, the process of the present invention can be conducted batchwise or continuously In a continuous process, for example, carbamate in the form of powder or in the molten state or in the form of a mixture with an inert solvent is loaded into at least one reactor which has been previously charged with a given amount of catalyst and, if

  appropriate additional inert solvent and which has been

  The reaction temperature must be sufficient, in the absence of a solvent, to allow the liquid phase thermolysis reaction to be carried out, that is to say at the same time. Above the melting point of the carbamate charge and product isocyanate product. Thus, a liquid phase can be achieved by dissolving the carbamate in a solvent as described herein or by fusing the carbamate in the absence of a soil

  If the alcoholic co-product boils lower than the iso-

  cyanate, which is the preferred case, the alcohol can be either removed by distillation of the solvent as it is formed or driven off with an inert gas

  (such as nitrogen, argon, carbon dioxide,

  bonique, methane, ethane, propane and their mixtures)

  that is passed into the solution, for example through

  to a sintered disc or similar device for the dispersion, or using a solvent boiling between the isocyanate and the alcohol and distilling between the boiling points of the isocyanate and the alcohol The recombination of isocyanates is thus

  minimized The use of a training gas is

  particularly appreciated in the absence of a solvent for

  facilitate the elimination of the alcoholic product.

  Alternatively, if the alcohol boils higher than the generated isocyanate, it can be recovered as described above with respect to the alcohol formed as a by-product When a polymeric aromatic isocyanate is formed this option is not available, since the polymeric isocyanate is not volatile at the reaction temperatures In this case, the catalyst and the solvent can be removed from the reaction mixture by any means capable of obtaining this effect. The catalyst and the solvent can be removed at the top by distillation. Thus, for this embodiment, a catalyst is chosen which is sufficiently volatile to vaporize at the distillation temperatures.

  alternatively, the solvent is removed at the top and the catalyst

  The polymer is removed from the reaction mixture by contacting the polymeric isocyanate with a suitable extraction solvent such as hexadecane, in which the catalyst is preferentially soluble or which contains a complexing agent. It may even be desirable from the point of view

  to avoid the removal of the catalyst from the iso-

  polymeric cyanate expected that these catalysts can also be used as catalysts in the formation of a final product of the type of a polyurethane. The reaction conditions are advantageously adjusted so as to obtain a degree of conversion as high as possible to avoid the need to separate

  polymeric aromatic isocyanate, the polybasic carbamate

  This can be achieved by raising the amount of catalyst and / or the degree of elimination

  alcoholic co-product However, since the

  Although the polymeric aromatic mate is less soluble in the solvents described herein than is the polymeric aromatic isocyanate product, the separation of the polymeric carbamate from the product polymeric isocyanate can be accomplished by extraction techniques. to solvent that use these solubility differences when the reaction is conducted at a low conversion rate Virtual elimination

  identifiable by-products makes this technique extremely

simple way.

  An unreacted carbamate can be

  collected and charged to a second reactor or recycled.

  In addition, it was found that the performance of the

  However, in some cases, commercially available carbamates may contain impurities which disadvantageously precipitate during the reaction. The process of the present invention, for the pyrolysis of polymeric aromatic carbamates to the corresponding polymeric isocyanates, can be incorporated into the multi-step process described in United States Patent Application No. 343,583 filed January 28, 1999. 2 for 2 l production of carbamates and polymeric aromatic isocyanates from

alkylated aromatic compounds.

  The multireaction stage process mentioned above comprises the following successive steps: ammonoxidation of an alkylated aromatic compound to form a nitrile, hydrolysis of the nitrile to an amide, conversion of

  of the amide into a carbamate, for example by

  Hoffmann position, carbamate condensation with an aldehyde to form a polycarbamate and, where appropriate,

  decomposing the polycarbamate to a polyisocyanate.

  The present invention is of particular interest in the multireaction process above as a

  that an improved method of decomposing the aromatic carbamate

  polymeric material to the polyisocyanate aromatic poly-

corresponding metric.

  The invention is illustrated by the following non-limiting examples, in which all parts and percentages are by weight,

unless otherwise specified.

  In the examples which follow, the apparatus used for carrying out the reaction consists, unless otherwise specified, in a 100 ml three-necked round bottom flask with reentrant tips, equipped with a high temperature heating mantle "Glas Col "(registered trademark) and a bar of magnetic stirrer A thermometer

  is connected by an open U-shaped tube to

  adding the components of the reaction mixture which are introduced with a syringe through a rubber membrane disposed on the other opening of the

  "U" The central neck is equipped with two super condensers

  15.24 cm, water-cooled, through which gas escapes The upper condenser is able to collect condensed liquids to prevent contamination of the

  reactor by the possible reintroduction of condensed alcohol.

  Nitrogen is dried by passing through a "Linde 4 A" (trademark) molecular sieve bed after passing through a "Drierite" (registered trade mark) column and is introduced below the level of the reaction liquid. The gases leaving the reaction apparatus also pass through a column of "Drierite" (deposited mrarch) which also includes a slight positive nitrogen current from a bubbler. The aim is to prevent air from entering the reactor. balloon when the nitrogen addition tube is opened for sampling Nitrogen flow is carried out using a "Flowrater" tube (trademark of Fisher-Porter) which has been calibrated to a measuring device

  The temperature is adjusted using a

  a thermoregulator based on the measurement of IR 2.

EXAMPLE 1

  The following example is intended to illustrate the effect of various catalysts on the rate constant of

  first order for the pyrolysis reaction.

  The general procedure for carrying out the reaction is as follows: 50 ml of solvent are charged into a dried flask, purged with nitrogen, as described above. The solvent (in this case tetraglyme) is then preheated to 200 ° C. It is then added to this flask over a period of one to two minutes, g (31 mmol) of methylenediphenylenedicarbamate (MDC).

  and a sufficient amount of catalyst for there to be a concentration

  Approximately 10 mole percent based on moles of carbamate. Samples of product isocyanate are periodically removed from the flask and deactivated by addition to a solution of dibutylamine (referred to herein as DBA) in tetraglyme. used as a solvent (10% DBA by weight of solution) to form a urea derivative from the isocyanate present in each sample This derivative, which gives an indication of the number of moles of the isocyanate formed, is analyzed means of a liquid chromatograph

  Hewlett-Packard 1084 B (called HPLC)

  after) on a C 8 reverse phase column using mobile phases of water and acetonitrile The last sample is taken after about 120 to 180 minutes of reaction The sample analysis is also confirmed by infrared analysis of the solution of

  product containing isocyanate and by comparing the iso-

  cyanate obtained in the sample with a control sample. A straight line of the logarithm of the isocyanate concentration (determined by HPLC analysis) is plotted versus time. The first-order rate constant is determined from the slope of this line. First-order rate constants for the various catalysts used together with the amount of MDC determined according to the above procedures are summarized in Table I. One of the tests is

  conducted in the absence of catalyst, for reference.

TABLE I

  Catalyst Test * No-first-order rate constant K 1 (min at 200 C) 1 None 0.0134 2 Bu 2 Sn (O Me) 2 0.0247 3 Sb (O Me) 3 0.0276 * Bu = Butyl Me = methyl. From the above rate constants, it can be seen that the catalysts substantially improve the

  rate of the pyrolysis reaction at 200 C.

EXAMPLE 2

  Charge at atmospheric pressure in a

  nitrogen purged 100 ml flask, equipped as described above.

  above, 4.58 g (30 mmol) of methyl N-phenylcarbamate, 2.94 g of chlorobenzene as internal standard, 0.89 g of dimethoxylate dibutyltin as catalyst and ml of 1,2-dichloroethane as solvent. at reflux (88 ° C.) at atmospheric pressure and slowly distilled overhead over a period of 75 minutes, 8 ml of solvent containing methanol A sample of the undistilled product is analyzed by gas chromatography (GC below) L analysis of the sample shows that 5.2 mmol of phenylisocyanate were formed at a selectivity of 99 mol% and a degree of conversion

17.3 mole%.

EXAMPLE 3

  The procedure of Example 2 is repeated, except that 1,2-dichloroethane is replaced by toluene. The reaction is carried out for a period of 40 minutes at a temperature of 870 ° C. Toluene forms an azeotrope with methanol. and facilitates its elimination

  of the reaction mixture The selectivity towards the phenyl

  isocyanate is 99 mol% and the conversion rate

1 o is 33 mol%.

EXAMPLE 4

  15.23 g of methyl N-phenylcarbamate and 0.8137 g of dibutyltin dimethoxylate are loaded into a 50 ml 3-neck flask equipped with a thermometer (thermoregulator), a magnetic stirrer, a column distillation system with discontinuous pressure drop and a nitrogen injector The mixture is heated at atmospheric pressure in the range of 100 to 1200 C in 3 hours

  by injecting nitrogen After 3 hours of reaction, the analysis

  lysis CPG shows a selectivity towards the isocyanate of

  phenyl 99 mol% and a conversion of 40 mol%.

  After continuing heating for another 3 hours,

  the selectivity is 95 mol% and the conversion rate

  During cooling, the solution is divided into two phases (i.e.

  solid phase and a liquid phase) To control the elimination

  methanol, a small amount of methanol is added. The liquid phase becomes entirely white and an exotherm temperature of 100 ° C is measured, indicating the presence of active isocyanate groups. This example demonstrates that the thermolysis reaction can be

  in the absence of a solvent and that at concentrations

  of the carbamate constituting the charge, an isocyanate can be generated as a product without the formation of undesirable by-products

  reduced temperature used for easy nitrogen injection

  However, in the absence of a solvent, the carbamate must be in the liquid state

  under the conditions of the reaction.

EXAMPLE 5

  1.0 g of methylene dimethylcarbamate are dissolved

  diphenylenediisocyanate in 50 ml of 1,2-dichloroethane and the solution is heated under reflux (88 ° C.) at atmospheric pressure. 0.09 c of dipropyltin dimethoxylate is added at reflux. GPC analysis of the product solution after 13 minutes of The reaction shows a significant conversion to diisocyanate-methylenediphenylenediisocyanate with no identifiable by-products. This example illustrates that the carbamate groups react independently and that the conversion of a carbamate group to its corresponding isocyanate does not affect the transformation of other groups. Therefore, the thermolysis reaction can be considered as a series of first-order reactions, each carbamate function acting independently. This applies to any polyfunctional carbamate of the type described in US Pat.

present memory.

  This example also demonstrates that the thermolysis reaction can be conducted at low temperatures,

for example at 88 C.

  It goes without saying that the present invention has been described only for explanatory purposes but in no way limiting, and that many modifications can be made to it.

without leaving his frame.

Claims (1)

1 process for the production of at least one aromatic isocyanate from at least one aromatic carbamate represented by at least one of the formulas: R-4 NHCOOR 2) (i) n and (X; N AAr) R 3 ## STR5 ## wherein formula II represents a mixture of carbamates; in formula I R 1 is a monovalent, divalent or trivalent aromatic hydrocarbyl group containing from about 6 to about 32 carbon atoms; R 2 is a monovalent hydrocarbyl group selected from saturated, saturated aliphatic or aromatic aliphatic hydrocarbyl groups, said hydrocarbyl groups having not more than about carbon atoms; and N is a number from 1 to 3 corresponding to the valence of R 1; and in formula II X is the monovalent group -O HCOOR 2 wherein R 2 is as defined for formula I; R 3 is independently selected from (a) a straight chain or branched chain divalent saturated aliphatic group having about 1 to about 10 carbon atoms, (b) a saturated divalent alicyclic group having about 4 to about 10 carbon atoms and (c) a divalent aromatic group having about 6 to 14 carbon atoms; Ar is a substituted or unsubstituted aromatic hydrocarbyl group having 6 to 14 carbon atoms, said substituents being selected from a halocene, an -NII 2 group and mixtures thereof; and n "is a number whose average numerical value in said mixture can vary from about 2.0 to about 3.5, and n is a number of about 1 to about 4, characterized in that it consists of (1) heating in the liquid phase to one of said carbamates in the presence of a metal-containing catalyst, said metal being selected from the group consisting of Ti, Sn, Sb, Zr and mixtures thereof, in conditions and in a manner sufficient to thermolytically transform said carbamate into at least one isocyanate, and at least one alcohol, said heating being conducted at a pressure at least equal to atmospheric pressure and said catalyst being effective to accelerate the speed of the thermolysis reaction with respect to the rate of the thermolysis reaction in the absence of a catalyst, and (2) separating said alcohol from said isocyanate and recovering the isocyanate 2 Process according to claim 1, characterized in that the heating is t is conducted by dissolving said carbamate and a metal catalyst containing a polar organic compound in an inert organic solvent to form a heated solution. Process according to claim 2, characterized in that the catalyst is represented by the formula (R 4) 4 Sn (B) a wherein R 4 is a hydrocarbyl group independently selected from an alkyl group of from about 1 to about 18 carbon atoms and an aryl group having about 6 to about 14 carbon atoms; B is independently selected from halogen, alkoxy having from about 1 to about 8 carbon atoms, alkanoyloxy having about 1 to about 8 carbon atoms, oxo and hydroxy, and "a" is a whole number from 1 to 3; and the inert organic solvent is selected from hexadecane, chlorobenzene, o-dichlorobenzene, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, dichloronaphthalene, methoxynaphthalene and the like. mixtures. Process according to Claim 3, characterized in that the carbamate is represented by the formula I. Process according to Claim 3, characterized in that the carbamate is represented by the formula II. Process according to one of Claims 4 and 5, characterized in that the solution which is heated comprises about 50 to about 98% by weight of inert organic solvent, based on the total weight of the solvent plus carbamate, and about 0.001 to about 0.3 mole of metal in the catalyst per mole of carbamic ester group carried by the carbamate. A process according to claim 6 in accordance with claim 4, characterized in that the solution is heated to a temperature of about 50 to about 200 ° C, preferably about 80 to about 150 ° C. 8 Process according to claim 7 in accordance with claim 5, characterized in that the solution is heated to a temperature of about 50 to about 300 ° C, preferably about 80 to about 180 ° C. The process of claim 5, characterized in that the carbamate of formula II, n is 1, R 3 is methylene and the average value of n is from about 2.2 to about 3.0, with R 2 being preferably methyl. Process according to one of the claims   1 and 2, characterized in that the catalyst is selected from the group comprising tetra-2,4-pentanedionate   of zirconium, tributoxyantimony, tetrabutoxy-   antimony, tetrabutoxytitanium, tetrapropoxyzirconium, tetraoctyloxytitanium, butylhydroxyoxotin,   dipropyldimethoxytin, dibutyloxotin, tributyl-   methoxytin, triphenylhydroxytin, trichloromethyl-   tin, dibutyldimethoxethane, tributylmethyloxy-   tin, trimethylhydroxytin, dichlorodimethyl-   tin, trimethylchlorotin, triphenylethanoyloxy   tin, diphenyldichlorotin, tin tetrachloride,   tin dichloride and mixtures thereof.