CA1054633A - Diamides of dicarboxylic acids - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
This invention relates to an improved process for the production of diamides of aromatic or cycloaliphatic dicarboxylic acids by subjecting an oligoester or poly-ester of a corresponding dicarboxylic acid to ammonolysis wherein the oligoester resp. the polyester is reacted with ammonia in a polyhydric alcohol at temperatures in the range between 30 to 200 and at partial pressures of ammonia in the range from 0,1 to 50 ata.

Description

1~54633 This invention relates to a process for the produc-tion of aromatic and cycloaliphatic dicarboxylic acid diamides by the ammonolysls of oligomeric or polymeric diesters of the corresponding dicarboxylic acids. ~ ~' It is known from British Patent ~o. 829,251, that benzene carboxylic acids or their lower alkyl esters can ' be heated with anhydrous ammonia in an autoclave at temp-~, eratures in the range from 150 to 350C. For example, ' ' terephthalic acid, isophthalic acid or terephthalic acid , , ,` 10 diethyl ester can be converted into terephthalic acid or ' ~' ,,~ isophthalic acid diamide by this known process at'tempera~
j~ tures,in the range from 250 to 280C and under pressures '"''--~
'i of the order of 160'atmospheres. Unfortunately, only 80 ''' ,,~
~, to 92% of the reaction mixture obtained consists of diamide. '`~' l~ In addition to diamide, the reaction mixture also contains '~,;,, "~ ammonium salts, monoamide, dinitrile and unreacted dicar-,i boxylic acid. Since difficulties are'involved in working ,'~
', ~ up reaction mixtures'of this kind, the process is not suitable for the production of pure diamides. Instead, the , ' :
20~ reaction mixtures obtainable by this process are ", ~ -' processed into nitriles by further heatin,g to a tempera~
- ture of from 350 to 500C. '`,~
,~ According to U.S. Patent No. 3,296,303, this process ~ ' ,l may be improved by using the ethylene glycol ester, pro~y~
I lene glycol ester or diethylene giycol ester of the dicar~
': . , , ~
,~, boxylic acid. In another embodiment of this known process ` ,' . , ¦ the free dicarboxylic acid is used as starting material ;~
and is initially reacted with excess ethylene glycol, ~ propylene glycol or diethylene glycol to form the corres~
'' 30 ponding diester. The reac~ion mixture obtained is ' ,1 . :
',''', . ~ ,' ' '' 2 ' ...... .. .. . . .

subsequently subjected to ammo~lysis, the excess glycol serving as reaction medium.
It is known from German Offenlegungsschrift No. ~;

2,216,116 that terephthalic acid diamide can be obtained by the ammonolysis of polyesters of terephthalic acid.
In this process, ammonolys1s is carried out either in the liquid phase at 70 to 125~C under ammonia pressures of from 30 to 100 atmospheres, or in the gas phase at 70 to 250C underammonia pressures of from 10 to 50 atmospheres.
In either case, ammonia is used in a large excess in order to obtain the high ammonia partial pressure required for a satisfactory reaction velocity. On completion of ammonolysis, the excess ammonia ! iS removed in gaseous form, condensed and recyclèd. -In the process described in German Offenlegungsschrift !~
No. 2,216,028, unsubstituted and substituted terephthalic :: .
acid and isophthalic acid diamides are obtained by polycondensing and corresponding dicarboxylic acids with i`
a dihydric or polyhydric alcohol or with a bisphenol or ~20 with mixtures thereof in the presence of a catalyst, removing excess polyol and water of reaction from the , oligomeric or polymeric esters obtained and subsequently treating them dirèctly with ammonia in the absence of any Poreign substances or auxiliaries. Ammonolysis may ~ ~
be~carried out either in-the liqu1d phase or in the gas ~ ~ ;
, .
phase in the manner already described in reference to Offenlegungsschrift No. 2,216,116. In cases where ammono~
lysis is carried out ln the liquid phase, the process is attended by the disadvantage that a fairly large excess of ammonia has to be used as solvent or as solution ::
. ~ .

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promoter for the polyester or oligoester. In cases where ammonolysis is carried out in the gas phase, the ~' ~¦ process is attended by the disadvantage that intensive ;
¦ mixing and relatively long reaction times are required ;~
¦ on account of the poor mass transfer. ~
It has now surprisingl'y been found that the ammonol- ';- ~' ;
ysis or aromatic and cycloal'iphatic oligoesters and polyesters uncler certain conditions in polyhydric alcohols ~' gives quantita-tive yields of diamides in short reaction -`~
'times. Accordingly, the present invention relates to a ;i ' process for the production of diamides of aromatic and cyeloaliphatic dicarboxylic acicls by the ammonolysis of '~
an oligoester or polyester of the corresponding dicarboxy~
~; ~ ~ lic acid with a polyhydric al'cohol, distinguished by the , ~ 15 fact thàt ammonolysis is carriecl out in a polyhydric ;~ ~ alcchol at temperatures of from 30 to 200C and under `~
'~ ammonia partial pressures of from O.l to 50 atmospheres. ' ~' Ol1goesters and polyesters of the follo~in~ dicar-boxyllo acids ma~ be used as starting materials in the ; process according to the invention: terephthalic acid, methyl terephthalic acid,~nitroterephthalic acid, 2,5- '~
dibromoterephthalic acid, l,~-dibromoterephthallc acid, tetrachloroterephthalic acid, tetrabromoterephthalic ~; aeid,~ tetrafluoroterephthalic acid, 5-bromo-2-nitrotere~
~ ~ 25 phthalic acid, 2-methoxy terephthalic acicl, 2,5-dinitrilo- "
'~ terephthalic acid, phosphonato terephthalic acid, '1~ 2-mcthoxy methyl terephthalic acid, isophthalic acid,

4-methyl 1sophthalic acid, 2j4,6-trinitroisophthalic acid, 4,6-difluoroisophthalic acid, isophthal-4 sulphonic aci~, isophthal-5-sulphonic acid, the isomeric naphthalene .. , ~:
.,, , . ' '~ ~, ' ~

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:

54~33 . dicarboxylic acids, aLso the 4,~ and 3,3'-isomeric diphenyl dicarboxy].ic acids, diphenyl ether dicarboxylic acid, diphenyl thioether dicarboxylic acicl, diphenyl ~ -~i sulphone dicarboxylic acid, diphenyl methane dicarboxylic i, 5 acid and diphenyl ethane dicarboxylic acid, also cyclo-~¦ hexane-1,4-dicarboxylic acid, cyclohexane-1,3-dicarboxylic -j acid and substituted derivatives of these carboxylic acids .;
i; with one or more alkyl, aryl, aralkyl, alkaryl, nitro, j sulphonic acid, sulphonate, hydroxy, alkoxy, cyano, amino .. :~
¦ 10 monoalkyl amino, monoaryl amino, dialkyl amino, phosphon-.ic acid, phosphonate, acyl or carboxylate groups as substi-: ~ tutents. Examples of polyhydric alcohols, from ~rhich the .. oligoesters and polyesters used are obtainecl are ethylene ~ .
.~ glycol, di.ethylene glycol, 1,3-propane diol, 1,4-butane ¦ 15 diol, 1,6-hexane diol, 1,8-oxtane di.ol, l,10-decane diol, 1,2-propane diol, 2,2-dimethyl-1,3-propane diol, 2,2,4- - :
trimethyl hexane diol, 1,4-xylene diol, 1,4-cyclohexa~e di.ol, 1,3-cyelohexane diol, cyclohe~ane-1,4-dimethanol ..
and glycerol. Other suitable starting materials are `:1: ' . .
oligoesters and polyesters of one of the above mentioned . ~.
~acids and several polyhydric alcohols, i.e. copolyconden-sates. Other suitable starting materials are mixtures ¦ eonsis-ting of different oligomers, different polymers or of oligomeric and polymeric homo- or co-polycondensates I ~:
o:f the same dicarboxylic acid. It is preferred to use ~ oligo- and poly-condensates of terephthalie acid, isophtha-~ lic aeid, methyl terephthalic acid, 2,6-naphthalene .
dicarboxylic acid, diphenyl 4,4'-dicarbo~Yylic acid, dipheny]
ether-~1,4'--dicarboxylic acid, diphenyl thioether-4,4~

1 30 dicarboxylic acid, diphenyl methane-4,4'-dicarboxylic acicl ~-',~ , :
-~
;' ~T -5-, . ~ ,; , ,, .,. , , , : ::

1~54~i33 ~.
': .`.~
; diphenyl ethane-4,~ dicarboxylic acid, diphenyl sulphone ~; ;

~,4'-dicarboxylic acid and of cyclohexanc-1,4-d.carboxyl ~-... . . .
ic acid, ~ith ethylene glycol, 1,4-bu-tane diol or gl,yoerol.
The ammonolysis reaction is carried out in the poly~
hydric alcohols mentioned above as ester component, i.e. ~ ;
ethylene glycol, diethylene glycol, 1,3-propane diol, 1,4- ~ -~; butane diol, 1,6-hexane diol, 1,8-oxtane diol, l,10-decane diol, 1,2-propane diol, 2,2-dime-thyl-1,3-propane diol, . ~2,2,4-trimethyl hexane diol, p-xylene diol, 1,4-cyclohexane diol, 1,3-cyclohexane diol, 1,4-cyclohexane dimethanol and glycerol. It is also possible to use mixtures o~ these ~ `- ~;
alcohols. ~he polyhydric alcohol which -forms the alcohol componellt of the ester is preferably used as reaction -medium;
~; lS In one preferred embodiment of the process according to the invention, an oligomeric or polymeric ethylene glycol ester of the dicarboxylic acid is used as starting mate~rial ~nd the ammonolysis reaction is carried out in e~thylene glycol.
20~ ~ rhe polyesters are used,~for~example, in granulate form, in chip -form or in fibre;form. Suitable starting materials are also the oligomeric and polymeric waste ~r~
,f ~ accumulating during the production and spinning of poly~
esters and during the chemical and mechanical after-treat-~ ment of polyesters. In addition to transesterification and polycondensa-tion catalysts, products of this kind may also contain antistatic agents, stabilisers, pigments and other additi~es, although there is generally no need to ; :
separate off the catalysts and additi~es because they have' ~ ss little or no eftect upon the ammonolysis reaction.

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r~~

9L633 `~ ~ -.
Instead o~ using the oligoesters and polyesters er se it is also possible to use the reaction mixture contain~
ing excess diol which accumulates during -their production. ~ -In this case, the excess diol is not separated off, as in ' 5 the process according to Offenlegungsschrift No. 2,216,028, 1 bu-t instead the reaction mixture is directly subjected to ammonolysis. `
¦ It has surpris~lgly been found that the polyhydric `i¦ . alcohols have a very favourable effect upon the ammonoly~
- 10 sis of oligoes-ter and polyesters, especially in regard to ` 3 selectivity. The quantity o-L solYen-t used is determined by the solubility of the product to be subjected to ammonolysis under the reaction conditions. In the case of oligomeric and-readily soluble polymers, the solvent may be used in such a quantity that a clear solution is ~;
~; present at the beginning of the reaction. In the case of substantiailly insoluble starting materials, the solvent ls used in such a quantity that the reaction mixture remains sufficiently fluid until ammonolysis is over, so that ~ ;
~- 20 adequate admixture is guaranteed. The quantities of solvent :` J ~ required are in the range of from 100 to lOOO~o by weight `
~j based on the oligoester or polyester used. The solvent is :~ ~:. ~ : ,:
preferably used in a quantity of from 200 to 500% by ~eight .~;~
based on the oligoester or polyester used. ~-In the process according to the invention, the reaction temperatures may be in the range from 25 to 200C.
Preferred reaction temperatures are in the range from 50 to 160C. The ammonia partial pressures are in the range ! from 0.1 to 50 atms. For teclmical and economic reasons ; ; ~
, 30 the process according to the invention is pre~erably carried out under ammonia ! :~
~ c~r _7_ ~54633 ` ~:
partial pressures below 20 atmospheres.
The necessary reaction time is governed by the type of oligoester or polyester used, by the ammonia partial pressure and by the reaction temperature and, in cases where an oligoester or polyester suspension is subjected to ammonolysis, is critically determined by the thickness of the starting materiàl as well, i.e. by lts grain size, by the chip diameter or by the fibre denier. In cases where .
ammonolysis is carried out in solution or in the case of a very finely divided material, it is generally over in less ~ -~
than two hours under the preferred reaction conditions. In ;~
the case of a very coarsely divlded material, the reaction times are longer, a polyester with a grain size of 5 mm - : ~. .
requiring a reaction time of 5 to 6 hours for example. ~ ;~
trhe process according to the invention may be carried ~ -out for example by initialiy dissolving or suspending the oligoester or polyester in the polyhydric alcohol and -subsequently introducing gaseous ammonia into the solution, or passing it through th~ suspension; with thorough stirring under~the reaction conditions, It is also possible to ~;~ introduce the solution or suspension lnto an autoclave, to fill the gas compartment of the autoclave with the necessary quantity of ammo~ia and intensively to mix the ; contents of the autoclave.
In cases where very coarsely divided polymer material is used, it is advisable initially to dissolve it in the polyhydric a ~ oh\ol at a temperature above the proposed reaction tempera ~ ré, and then to leave the resulting solution to cool down to room temperature. Unless it remains completely dissolved, the polyester is precipitated in finely .,~

, . , .. . , , . , ~ , i

5~633 ~ :

divided form and, hence, becomes more readily accessible I
to attack by -the ammonia. In this l~ay, short reaction times can be obtained cven ~:ith coarsely divided starting material.
In general, the diamide is substantially insolub]e in the polyhydric alcohol. It precipi-tates either during the reaction or, at the latest, on completion of the reaction and after cooling of the reaction mixture. It is ex-tremely - ~ pure and may readily be separated off by filtration or ; 10 centrifuging. In some cases, it is of advantage to improve the Iilterability of the diamide by the addition of an inert solvent such asS for example, acetone. That part of the - diamide which does not precipitate after cooling of the ~` reaction mixture may either be separated off from the ~-mother liquor or may be recycled with it.
The advantage of the process according to the invention `, .. - ~ ~
over the processes knol~n from the Offenlegungsschrifts Nos. 2,216,028 and 2,216,116 is that ammonolysis can be ! carried out under lol~ pressures. In addition, the diamide j.
after its ~ormation, precipitates in high yields from the ¦
reaction mixture in the form of a highly pure solid ~hich ~-~
is free both from starting materials and from secondary products~ Accordingly, the diamide may readily be separated off by filtration or centrifuging. Whereas, in the conven-tional process, the excess ammonia has to be removed and condensed before it can be reused, it remains largely dissolved in`the polyhydric alcohol in the process according .
to the inven-tion and may be recycled together with the polyhydric alcohol. In addition, the quantity of ammonia required is smaller tllan in the conven-tional process.
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, ....... . . ..... .~ . .

1~54633 250 g (1.30 mol) of ground polyethylene terephthalate (average grain diameter ~ 0.5 mm) were suspended in 750 g of ethylene glycol in a heatable l-litre-capacity glass auto- ~ -~
clave equipped with a stirrer. The autoclave was heated to 140C and placed under a pressure of 9 atmospheres by the introduction of ammonia gas. The contents of the auto-clave were continuously stirred and left for three hours ~-under the above-mentioned conditions. After cooling and venting of the autoclave to normai pressure, the reaction suspension was filterad and the filter residue washed twice ;-~,;
with 400 ml of water and 400 ml of methanol. The residue - ~ ;
was dried in vacuo at 60C, giving 203.5 g (95.3% of the theoretical) of pure terephthalic acid diamide.
EXAMPLE 2 ;
Using the apparatus described in Example -1, 250 g (1.30 mol) of polyethylene terephthalate granulate tgrain ~-diameter 5 mm) were suspended in 750 g of ethylene glycol , and the resulting suspension heated to 235~C. The polyester ~ -completely dissolved at that temperature. The solution ~ -was then~cooled to 140C the polyester precipitating down again in fine form. Ammonia was then introduced into the suspension as in Example 1, followed by stirring for 2 hours at 140~C/9 atmospheres. The autoclave was then cooled and . ~ , vented and the reaction p~oduct worked up as in Example 1 -giving 205 g of pure white, powder-form terephthalic acid diamide (96% of the theoretical).
EXAMPLE 3 ~-215.8 g tl.30 mol) of terephthalis acid, 1000 g tl6.13 mol) of ethylene glycol and 0.5% by weight of antimony tri-oxide, based on terephthalic acid, were heated under reflux ,, - 10 - ~ ~ ' ,. : . .

1~54633 ~

with stirring rOr 1 hour at a temperature of from 190 to 195C. 600 g oI glycol/water (approximately 47 g of water of reaction) ~rere distilled off under normal pressure over ,~
a period of 5 hours, The oily residue, an oligomer mixtuYe in eæcess glycol, was transferred to the autoclave, des- ';cribed in Example 1, tempered at 140C and ammonia intro~
duced. The con-ten-ts of the autoclave were stirred for 3 :
hours under a pressure of 9 atomospheres 9 after which the ~`
autoclave was cooled and vented. The reaction suspension ., :
, 10 formed was worked up in the same way as in Example 1, giv-ing 198 g (93~0 of the theoretical) of pure terephthalic acid diamide, ~ -~:: ~:'~
XA~P~E ~
In the apparatus described in ~ample 1, 250 g (1.30 mol) of powder-form polyethylene terephthalate were suspended in 750 g of glycero] and the resulting suspension heated t,o 140C, after which the autoclave was placed under a pressure of 9 atomospheres by the introduction of ammonia, ~he reac-tion mixture was stirred for 12 hours under these condi-tions ',~ `;
, aPt~er which the autoclave was coole~d and vented. In order '~
to improve filterability, 500 ml of acetone were added to .
the reaction suspension which was then filtered off, washed with 200 ml of water and acetone and finally dried. Pure ~ terephthalic acid diamide was obtained in a yield of 188 g ~ ~ -(88~ of the theoretical).
EX~MPLE 5 ,~
125 g (0.568 mol) of a polyester of terephtllalic acicl and 1,~l-butane diol were suspenfled in 400 g of 1,4-butane diol, the resulting suspension treated with ammonia for 12 hours at 140C/9 atmospheres, followed by working up in the same way as in Example l~. Extremely pure terephtllalic acid diamide was obtained in a yield of 88g(91l,5~ O:r the C~ theore l;iC.l~ ].1-. ,~ .. .,., .. ,~, -, . , . :., , 10~i4633 125 g of a polyester of terephthalic acid and ~-xylylene diol were suspended in 300 g of glycol and the resulting suspension treated with gaseous ammonia in the same way as described in Example 1. The temperature was 140C, the precsure 6 atmospheres and the reaction time 8 hours.
Yield of terephthalic acid diamide: 76.5 g (92% of the theoretical). -215.8 g (1.30 mol) of isophthalic acid and 1000 g ~;
(16.13 mol) of ethylene glycol were converted as in Example 3 into a highly viscous oligoester mixture, dissolved in excess ;~
ethylene glycol, which was then treated with ammonia in ~ the apparatus described in Example 1. The reaction temperature i for the ammonia treatment was 120C, the NH3-pressure 9 ~ atmospheres and the reaction time 4 hours. Working up gave 1 185 g of pure i90phthalic acid diamide (86.8% of the theoretical). Another 23 g (10.8% of the theoretical) of ~isop~h~halic acid diamide could be detected in dissolved ~ -form in the mother liquor.
;~ EXAMPLE 8 234 g (1.30 mol) Oe methyl terephthalic acid and 1000 g ~16.15 mol) of ethylene glycol were converted as in Example 3 ~ ~ -into an oligoester mixture, dissolved in excess ethylene ~ glycol, and subsequently treated with ammonia in the apparatus ,~ described in Example 1. The reaction temperature~was 140~C, the NH3-pressure 9 atmospheres and the reaction time 10 hours.
The product was filtered off, washed with methanol and water and dried. Pure white; powder-form methyl terephthalic acid diamide was obtained in a yield of 130 g, corresponding .

': .'' ' :

~54633 :
`~ .
to 56~o Of -the theoretical. ~nother 40 g of methyl tere-phthalic acid diamide (17.4~o Of the theoretical) crysta:Lli-;
sed out over night from the IICl-neutralised mother liquor consisting of glycol, water and methanol. Einally, a resiaue of 50 g (21. 6~o of the -theore-tical) could be detec-- ted in the mother liquor. ~ccordingly, the total yield amounted to 220 g (95~D of the theoretical).

224 g (1.30 mol) of cyclohexane-1,4-dicarboxylic acid and 1000 g of ethylene glycol were converted as in Example 3 into an oligoester mixture, dissolved in excess ethylene glycol, and subsequently treated with ammonia in the appara-~. -tus described in Example 1. The reac-tion temperature was ~ ~;
~ 120C the N~I3-pressure 9 atmospheres and the reaction time 10 hours. ~he autoclave was then vented and cooled to room `~
tèmperature. 220 ml of acetone were added to the reaction `~
suspension containing approximately 400 g of glycol, follow-, : .
~d by filtration and washing with 200 ml of water and 100 ml ~ of methanol. After drying, cyclohexane-1,4-dicarboxylic acid diamide was obtained in extremely pure form in a yield `~
of 195 g (87.2% of the theoretical~. -More (lO~o of the ;~
theoretical) cyclohexane-1,4-dicarhoxylic acid diamide could be detected in dissolved form in the mother liquor. ;~
EXAMPLE ]0 280 g (1.30 mol) of napthalene-2,6-dicarboYylic acid and 1000 g of ethylene glycol were converted as in Example 3 into an oligoester mixture, dissolved in excess e-thylene ::.
glycol, and subsequently treated with ammonia in the appara~
tus described in Example 1. The reaction temperature was 1/l0C, the N~I3-pressure 9 atmospheres and the reaction t:ime `-15 hours.

.. . . . .

After the autoclave had been vented and cooled, 200 ml of acetone were added to the reaction suspension, followed by filtration and washing with 200 ml of water and 100 ml of methanol. After drying, naphthalene-2,6-dicarboxylic acid diamide was o~tained in a yield of 208 g (75% of the theoretical). Another 11 g of diamide (4% of the theorectical), 11% of the theoretical (37 g) of naphthalene dicarboxylic acid glycol ester amide and 10% of unreacted oligoester were detected in dissolved form in the mother liquor. -~

168 g (0.65 mol) of diphenyl ether dicarboxylic acid and 1000 g of ethylene glycol were converted into an oligoester mixture dissolved in excess eth,ylene glycol in the same way as in Example 3, except that 800 g of glycol/water (approximately 23 g of water of reaction) were distilled off over a period of ~
7 hours. The highly viscous residue was transferred to the ;
autoclave described in Example 1, 300 g of fresh glycol were -~
added and the autoclave heated to 140C. Ammonia was ~hen introduced. The reaction temperature was 140C, the ~H3~
pre~sure 9 atmospheres and the reaction time 4 hours. After venting and cooling, 150 ml of acetone were added to the .
reaction suspension, followed by filtration and washing with water/methanol. The-yield amounted to 95 g (75.1%
of the theoretical). The mother liquor contained, in dissolved form, 5% of diamide, 5% of ester amide and approximately 30%
of unreacted oligoester.

130 g (0.65 mol? of chloroterephthalic acid and 100 g ~ ~ -of ethylene glycol were converted into an oligoester mixture dissolved in excess ethylene glycol, treated with ammonia and worked up in the same way as in Example 11. The yield ~ ;

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~(~5~;33 ,:
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I of precipitated diamide a~ounted to 81 g (64% o the ¦ theoretical~ The mother liquor contained 20~ of unreacted ;~I starting product, 6% of ester amide and 11V,~ of diamide.
i - EXAMPL}~ 13 ~ . . ~ . , . ~
S 215.8 g (1.3 mol) of terephthalic acid and 1500 g ! ~ . (10.h mol) of cyclohexane-1,4-dimethanol were reacted as in Example 3 in the presence of 0.5% by weight of antimony trioxide, based on terephthalic acid7 The resulting oligomer mixture in excess cyclohexane 1,4-dimeth2nol was transferred iO - t~ the autoclave described in Example 1, tempered at 140C ~ `
and ammonia introducedO The contents of the autoclave were ~, then stirred for 15 hours under a pressure of g atmospheres, b; ~ ollowed by cooling and venting. 1000 ml of methanol were then added and ~he fine reaction suspension filtered. The `~
filter residue was washed first with 400 ml of water and then with 400 ml of methanol The residue was then dried in vacuo at 60C, giving 201 g (94.4%of the theoretical) of pure terephthalic acid diamide.

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Claims (21)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A process for the production of diamides of aromatic and cycloaliphatic dicarboxylic acids by the ammonolysis of an oligoester or polyester of the corresponding dicar-boxylic acid with a polyhydric alcohol, wherein ammonolysis is carried out in a polyhydric alcohol at a temperature of about 30° to 200°C under an ammonia partial pressure of about 0.1 to 50 atmospheres.

2. A process according to claim 1, wherein said polyhydric alcohol of said oligo- or polyester is a dihydric alcohol; and said polyhydric alcohol of said ammonolysis is a dihydric alcohol.

3. A process according to claim 2, wherein said dihydric alcohol of said ester, and said dihydric alcohol of said ammonolysis are the same.

4. A process according to claim 1, wherein said oligo- or polyester is an ester of terephthalic acid, isophthalic acid, 2,6-naphthalene dicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, diphenyl ether-4,4'-dicarboxylic acid, diphenyl thioether-4,4'-dicarboxylic acid, diphenyl methane-4,4'-dicarboxylic acid, diphenyl ethane-4,4'-dicarboxylic acid, diphenyl sulphone-4,4'-dicarboxylic acid or cyclohexane-1,4-dicarboxylic acid.

5. A process according to claim 1 or 4, wherein said ammonolysis is carried out in a polyhydric alcohol selected from the group consisting of ethylene glycol, 1,4-xylene diol, 1,4-butane diol, cyclohexane-1,4-di-methanol and glycerol.

6. A process according to claim 1 or 4 wherein the oligo- or polyester is an ester of a dicarboxylic acid and ethylene glycol and said ammonolysis is carried out in ethylene glycol.

7. A process according to claim 1, 2 or 4 wherein said ammonolysis is carried out at a temperature of about 50° to 160°C.

8. A process according to claim 1,2 or 4 wherein said ammonia partial pressure is about 1 to 20 atmospheres,

9. A process according to claim 1, 2 or 3 wherein said temperature is about 50° to 160°C and said ammonia partial pressure is about 1 to 20 atmospheres.

10. A process for the conversion by ammonolysis of a polyester, which is the condensed oligomeric or polymeric ester of a cycloaliphatic or aromatic dicarboxylic acid and a polyhydric alcohol, into the corresponding pure diamide of said dicarboxylic acid, which process comprises: reacting said polyester with ammonia in a polyhydric alcohol as the essential liquid solvent reaction medium at a temperature of about 30° to 200°C and under an ammonia partial pressure of about 0.1 to 50 atmospheres.

11. A process according to claim 10, wherein said polyhydric alcohol of said polyester is a dihydric alcohol and said liquid solvent reaction medium is a dihydric alcohol.

12. A process according to claim 11, wherein said dihydric alcohol of said ester, and said dihydric alcohol solvent are the same.

13. A process as claimed in claim 10, 11 or 12 wherein the ammonia partial pressure is about 1 to 20 atmospheres.

14. A process as claimed in claim 10, 11 or 12 wherein the ammonia partial pressure is about 5 to 10 atmospheres.

15. A process as claimed in claim 10 wherein the dicarboxylic acid is terephthalic acid, isophthalic acid, 2,6-naphthalene-dicarboxylic acid, diphenyl-4,4'-dicarboxylic acid, diphenylether-4,4'-dicarboxylic acid, diphenylthioether-4,4'-dicarboxylic acid, diphenylmethane-4,4'-dicarboxylic acid, diphenylethane-4,4'-dicarboxylic acid, diphenylsulfone-4,4'-dicarboxylic acid or cyclohexane-1,4-dicarboxylic acid.

16. A process as claimed in claim 10 wherein the ammonolysis is carried out in ethylene glycol, xylenediol-1,4, butanediol-1,4, cyclohexane-1,4-dimethanol or glycerol as said solvent.

17. A process as claimed in claim 15 wherein the ammonolysis is carried out in ethylene glycol, xylenediol-1,4-, butanediol-1,4,cyclohexane-1,4-dimethanol or glycerol as said solvent.

18. A process as claimed in claim 10 wherein said temperature is about 50° to 160°C.

19. A process as claimed in claim 17 wherein said temperature is about 50° to 160°C.

20. A process as claimed in claim 15, 17 or 18 wherein the ammonia partial pressure is 1 to 20 atmospheres.

21. A process as claimed in claim 15, 17 or 19 wherein the ammonia partial pressure is 5 to 10 atmospheres.