IL31898A - Process for the preparation of isocyanates - Google Patents

Description

Procesa for the preparation of BAYER 30239 Prooess for the preparation of isocyanates It is known that isocyanates can he prepared reacting primary amines with excess first at temperatures near room temperature and then at increasing temperatures up to the boiling point of the solvent usually up to about 100 to and then slowly introducing phosgene into the reaction mixture until the reaction is In this seoond phase of the the hot hydrogen chloride is evolved and this escapes from the reaction mixture together with excess In known modification of instead of the free primary their usually the are ly converted by a hot phosgenation according to the second stage of the process described above into mainly hydrogen chloride being driven off in In this conventional industrial process the quantity phosgene used is 3 to 7 times the stoiohiometrioally calculated The hydrogen which is formed freque tly ses a highly undesirable corrosion of the apparatus in which the reaction is oonduoted and this accordingly necessitates ture on the Another serious disadvantage of the entional process for the production of isooyanates is the long reaotion time usually about 4 to 20 In DAS a process in isocyanates are prepared by phosgenation of primary amines in the presenoe of tertiary amines is Although this prooess affords certain the use of tertiary amines as auxiliary compounds entails considerable expenditure which again makes the teohnical advantages of this cess It has now surprisingly been found that primary amines oan be reacted with phosgene in the presence of aqueous solutions of inorganic and in the presence of hydrophobic inert io solvents to although it is known that nates are decomposed by water to form In it was feared that the aqueous alkaline solutions of phosgene would go extensive hydrolysis so that even in the unforeseeable event a successful isocyanate it was expected that a siderable excess of phosgene would be It is ly found that to the stoichiometrioal quantity phosgene is perfectly adequate in this One particular advantage of the process is also the short time needed for its The reaction proceeds so rapidly that it can be ried out Another advantage is the possibility of using the process according to the invention for preparing low boiling isocyanates such as ethyl and propyl isocyanate which were difficult or impossible to obtain by the usual phosgenation The present invention thus relates to a process for the paration of characterised in that primary amines are reacted with phosgene in the presence of aqueous solutions of organic bases and hydrophobic inert organic solvents at temperatures between and One of employ reaction peratures above or below these although the reaction peratures are preferably between and In isocyanates which are slow to reaot can be prepared at higher Especially high yields are obtained if no products which are only sparingly soluble in the solvents used are formed during the Examples of suitable starting materials for the invention are saturated aliphatic acyclic and such as methylamine 2 and tertiar hylene diamine 1 inol ne dienylene diamine exyl methane and 1 unsaturated aliphatic such as methallylamine and amines and such as and nd diamin polyamines such as and and and 2 4 diohenylmethane 1 and phosphoric acid etheramines a such as ethyl propyl phenetidi and amines and polyamines which contain ester such as methyl aminocaproate ethyl inoethylcarbonate and the aminoethyl ester of acrylic acid and methacrylic Mixtures of different amines may of be Sodium hydroxide and potassium sodium carbonate and potassium carbonate and rhosphates which are basic in reaction as examples of inorganic bases which are used as Suitable hydrophobic inert solvents hydrocarbons such petroleum chlorinated hydrocarbons such ethylene carbon chloro benzene and esters such ethyl acetate and butyl acetate or such as Water may be in which case an additional quantity of liquor equivalent to the amount hydrochloride must be but hydrophobic inert be included also in these As a the reaotion is oarried out by adding the amine a solution of the amine in an inert and the aqueous solution of the base simultaneously to absolution of phosgene in the inert organic solvent with stirring and During this the pH of the mixture is preferably maintained between 1 and 7 until all the amine has been and the solution is then made alkaline at the end of the The reaction ture separates into an aqueous and an organic phase after the The organic phase oontains the isooyanate which may be isolated in the usual by fraotional of the invention is particularly advantageous if the reaction of the primary amine with phosgene is carried out in the presence of aqueous solutions of inorganic bases and hydrophobic inert or anic solvents usin a reaction time of less than 1 The reaction times required are often only a few seconds or evert fractions of a This method procedure is very suitable for continuous Compared the usual production of this process affords the advantages of a very high yie and a substantial reduction in the corrosion of the Also the short reaction used permits rapid separation of the reactants and frequently enables the yields to be considerably increased with the yields are obtainable when the process is carried out using longer reaction The reactor used in this process may be any in which phosgene and an aqueous solution of an inorranic base can be intensively mixed in a short the the phosgene usually bein resen in the form of a solution in a hydrophobic organic For the reactants may vigorously mixed in a chamber or they may be sup inlet so very intensive mixing of the resulting liquid droplets takes Inert gases such as air or may be used as propellents for atomizing the and these gases may be It is also possible to carry out a combination of the mixing the amine solution and aqueous liquor first mixed as intensively as and then droolets of the with nitrogen as the carrier is then sprayed into the stream of this liquid mixture to cause the reaction itself to The reaction temoeratures are kept in the range of about to Preferably to by cooling the starting materials the mixing apparatus the propellent gas before a low boilin solvent which removes heat of reaction during the reaction by evaporation may also bo u The phases present in the reaction mixture arc separated as completely as possible after the a cyclone be used if desired for removing the and the liquid phases be separated in a separating vessel or using a The the phases be followed by drying the organic solution which contains the drying agents such as calcium sodium sulphate or a zeolit Azeotropic dehydration is particularly useful and be carried out in In this of drying is combined with isolation of the isocyanate since the crude isocyanate remains together with the solvent and may subsequently be if by The phosgene used is generally 1 to 5 times the molar quantit of the phosgene excess may be in the and used Amine and are ad antageously used in a of to a ratio of to being In many a molar rstio of amine to phosgene in the region of to has proved to be particularly The amount of aqueous liquor used is at least 2 moIs for 1 mol of Dosing of the materials is carried out dosing pumps and should be ss as The reaction is less than one minute and in some cases only a few seconds or fractions of The isocyanates obtained the process are intermediate for the preparation of synthetio resins and iary materials for synthetio resins and may used as as Example 1 120 g of phosgene are dissolved in 300 ml of at 73 g of tertiary butylamine dissolved in 100 ml of and 96 g of sodium hydroxide dissolved in 400 ml of water are introduced dropwise simultaneously into the tion of phosgene at 0 to over 30 The reaction ture is at the same time vigorously stirred and ooled to the en Afterthe the phases are separatedj solution of the isocyanate is dried over sodium sulphate and fractionally 72 g of the of iary butyl isocyanate of boiling point 84 to mm Hg are Example 2 164 g of an amine which is obtained by the Ritter reaction from hydrooyanio acid and sulphuric aci followed by hydrolysis of the resulting and which has a boiling range of to mm Hg and an tent of are added dropwise in the course of 25 minutes to a solution of 100 g of phosgene in 500 ml of methylene chloride at with stirring A further 20 g of phosgene are introduced into the reaction mixture during the addition of the At the same a solution of 130 g of sodium hydroxide in 600 ml of wate is added dropwise at such that a ring electrode indicates a PH of about 2 until the addition amine is the remaining sodium hydroxide solution is then added dropwise in the oourse of 15 minutes until a pH of is The phases are then The methylene ide after drying over caloium ohlo ide is fractionally After removal of the methylene chloride by distillatio followed by vacuum 154 g of the of an which has a boiling range of 65 to Example 3 177 g of g of sodium dissolved in 800 ml of water and 45 g of phosgene are added all together over 30 minutes to a of 130 g of phosgene in 500 ml of methylene Vigorous stirring is continued during the reaction and the temperature is between 0 and by After the 20 g of sodium hydroxide dissolved in 100 ml of water are added The phases of the reaction mixture are the organic phase is dried over sodium sulphate and the methylene chloride is distilled Crude which has an NCO content of remains Yield higher than of the Example 50 g of dissolved in 200 ml of methylene chloride are added dropwise between and with stirring and cooling to the mixture of a solution of 75 g of phosgene in 200 ml of methylene and 50 ml of At the same 175 ml of a sodium hydroxide solution are added dropwise at a rate that a measuring electrode tes values of 1 to 7 up to the end of the addition of the amine The addition of amine is finished after 15 The of the sodium hydroxide solution is added dropwise at sue h a rate that the reaction mixture has a pH of 6 to and towards the end 7 to The addition of sodium hydroxide solution is completed after 40 The phases of the reaction mixture are separated and methylene chloride solution is dried over sodium After removal of the methylene chloride by 60 g of crude remain NCO content yield above 97 of the theoretical Example 5 255 g of amine mixture which consists mainly of heptadecane and which has obtained from ketones of the fatty acid of coconut oil are added dropwise at about together with a solution of 160 g of sodium hydroxide in 400 ml of to solution of 150 g of phosgene in 500 ml of methylene The reaction mixture is also stirred vigorously and the sodium hydroxide solution is added at such a rate that after 15 minutes when all the amine has been added the pH of the mixture is 1 to After a further 25 the sodium hydroxide solution has been added and final pH value is The reaction is the isocyanate solution is dried over sodium sulphate and the crude isocyanate is distilled under 245 G a heptadecylisocyanate which boils in the range of 140 to mm Hg are NCO Content yield of the Example 6 150 g of phosgene are dissolved in 200 ml of methylene To thissolution is added a solution of 62 g of e diamine in 250 ml of methylene chloide with vigorous stirring over 15 minutes at and at the same time sodium hydroxide solution is added at such a rate that pH of the mixture kept between 2 and The remainder of solution of 140 g of sodium hydroxide in 400 ml of water is then added dropwise within the course of a further 20 minutes until finally of 13 is The phases of the reaction mixture are separated and the methylene chloride solution is dried over sodium sulphate and 48 g of ofhexa boiling in the range of 100 to mm Hg are NCO content Example 7 80 of hos ene are dissolved in 350 ml of tolu n a The solution is stirred with 50 ml of concentrated sodium chlorid solution and a measurement electrode is dipped into the 1 of methylamine are introduced over 20 minutes at to and at the same time a solution of 90 g of sodium hydroxide in water are added dropwise at such a rate that the pH measured is 4 When the addition of amine is more sodium hydroxide solution is added in the course of a further minutes until a pH of 10 is The phases of the reaction mixture are separated and the aqueous phase is extracted with The solution of the resulting methyl isocyanate in toluene is dried over The nate content is determined by reacting the product with a IN solution of dibutylamine in and titrating the reacted dibutylamine hydrochloric The toluene solution contains of socyanate this corresponds to g of of the Example 8 The a used carryinr out the process consists a of two In the first e solution aqueous alkaline liquor introduced through a dosing are intensively mixed and in the second c this two phase mixture intensively stirred wi h phosgene with the aid of a stream of nitrogen and allowed to leaving the mixing reaction products reach a cyclone separator in which the and as are separated from each The is trapped and the organic is separated from dried and distilled if desired under The residence time of the reactants in the reaction is to seconds in the examples A solution in chloride to and hydroxide cooled to the same temperature are forced under pressure into the first The stream of amine solution is adjusted to mols per the stream of lye to 16 mols per A solution of phosgene methylene chloride which has been cooled to to sprayed hrough a stream of nitrogen of 3 to snd the rate adjusted to 6 mols per The temperature of the reaction products after the mixing chamber is kept between 0 by cooling the starting before use and by evaporation of a part of the After 15 minutes the liquid phases trapped in the funnel are separated each ot and the orrranic phase dried with calcium chloride and G of are the throughput is 1 ol of his corresponds to a yield of 9 By the sarre process as described in Example of corresponding to a yield of are obtained by after a throughput of 1 mol of 10 Λ one molar solution of aniline used in the process given in After throughput of 1 of 114 g of to a yield of are obtained by 1 A one molar solution o is used by the same process as in Example After a throughput of 1 14 g of corresponding tc yield or obtained by Example half molar solution of hexamethylene diamine is used in same process given in Example After a throughput of half a of hexamethylene the phases are separated and the organic phase is recovered by G of lene diisocyanate corresponding to yield of are Example 15 A half molar solution of in methylene chloride is used in the same process described in Example After a throughput of half a two phases are separated the organic phase is dried over a zeolite and of methane correspondin to a yield of are The distillation residue is g this has an isocyanate determined by of 1 solution of in liouid propane and a hydroxide solution and a solution of phosgene in liouid propane are reacted together in a material mixing chamber with intensive mixing and to release of The heat or reaction is compensated by the evaporatio of phosgene and the methyl isocytnate and the temperature of the reaction products is adjusted to suitab choice of the quantities of and solution The concentrations of starting materials are chosen so that all the reaction products except the reacted sodium hydroxide solution which is removed in a cyclone separator After the cyclone these reaction are dried in a calcium chloride tower and then condensed in Gas chromatographic of the reaction products at to yield of methyl insufficientOCRQuality

Claims (8)

31898/2 %i

1. A process for the preparation of isocyanates, characterised in that prim ry amines are reacted with phosgene in the presence of aqueous solutions of inorganic bases, and hydrophobic inert organic solvents at temperatures between -30 and +35°0·

2. A process according to Claim 1, characterised in that a pH range of 1 to 7 is maintained during the reaction and a pH above 7 at the end of the reaction.

3. · A process according to Claim 1 or 2, characterised in that the reaction of the primary amine and the phosgene takes place within a time of less than one minute.

4. A process aocording to Claim 1, characterised in that the reaction of the primary amine and the phosgene —10 —2 takes place within a time of from 10 to 10 seconds.

5. A process according to any one of the preceding Claims, characterised in that amine and phosgene are used in the molar ratio of from 1:1 to Is20.

6. A process accordin to Claim 5, characterised in that amine and phosgene are used in the molar ratio of from Isl to 1*8,

7. · A process according to Claim 5» characterised in that amine and phosgene are used in the molar ratio of from Is to ls2.

8. A process for the preparation of isocyanates according to Claim 1, substantially as described and exemplified hereinbefore.