CA1064526A - Process for the preparation of pure'-tetramethyl-phenylene biscarbinols - Google Patents

Abstract

PROCESS FOR THE PREPARATION OF PURE ?,?,?',?'-TETRAMETHYL-PHENYLENE BISCARBINOLS
Abstract of the Disclosure A process for the preparation of pure ?,?,?',?'-tetra-methyl-phenylene biscarbinols by the oxidation of diisopropyl-benzenes at elevated temperatures with air or oxygen in the presence of aqueous solutions of strong alkalies, wherein the reaction mixture is freed from alkalies by washing with water, and ?,?,?',?'-tetramethyl phenylene biscarbinol is isolated by fractional distillation at pressures of at least 1 Torr and temperatures of at least 120°C.

Description

~i9L526 This invention relates to a process for the preparation of pure ~ te~ramethyl-phenylene biscarbinols (biscar binols) by the atmospheric oxitlation o~ diisopropylbenzenes in the presence of strong alkalies followed by isolation of the reaction product from the reaction mixture consisting of bis-carblnols, ~, ~ -dimethyl-isopropylphenylcarbinols (monocarbinols) ; and unreacted hydrocarbons.
Biscarbinols are important starting materials for the pre-paration of bisphenols and aromatic diamines which are required ~or the manufacture of high quality thermoplastic polyconden-~- sates, such as polcarbonates, polyurethanes, novolaks or curable resols. In addition, highly alkylated bi~phenols are very e~fec-tive stabilizers ~or polyurethanes.
Biscarbinols used for the purposes mentioned above are ~re-:i ji 15 quently required to have a high degree of purity. In particular, l~ the monocarbinols which occur as intermediate products o~ oxida-tion must be separated from the biscarbinols because they sub-stantiall~ reduce ~he properties o~ the above-mentioned poly-~ condensates produced ~rom the biscarbinols.
'~ 20 In order to obtain such highly purified biscarbinols, the un reao ted hydrocarbons and monocarbinols must be aeparated from the biscarbinols a~ter the alkalies requirecL for oxidation of the diisopropylbenzenes have been removed by washlng with water.
While there is no problem in separating the starting materials, Z5 the diisopropylbenzenes~ from the biscarbinols since they are ~;~ physically ancL chemically very different ~rom each other, no economical proc~ss has hitherto been available for s0parating monocarbinol~ ~rom biscarbinols.
;It 1s~known from German Ausle~eschri~t No. 1,253,692 that the simple proces~ for crystallising the biscarbinol from th~

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reaction mixture only yields a ~ery impure product. The biscar-binol content in the filter cake is in the range of from 22.5 to 64 % by weight. In no experiment it was pos~ible to reduce the monocarbinol content to an extent less than 28 % by weight.
Recrystallisation mus-t therefore be repeated several times to obtain pure biscarbinols, but such repeated recrystalli~ation entails high investment and manufacturing costs since each stage of reo~tallisation requires a complete crystallisation unit.
The energy costs are also considerable since at each stage of recrystallisation the product and solvent must be heated and cooled again. Furthermore, the sol~ent required ~or the process constitutes an additional component which must subsequently be worked-up7 and therefore further increases ~he necessary expen-diture in apparatus and the ene~gy co~ts.
On the other hand, separation of monocarbinols from bis-carbinols by distillation has hitherto been regarded as techni-i ;~ cally impracticable for various reasons. In order to expel mono-carbinols completely from bi3carbinols, th~ mixture h~s to ~e . ~
heated to the boilin~ point of the bi~carbinol At a pre~sure of 10 Torr, for example, the boiling point is about 170C, and at 20 Torr about 180C. At ~uch temperatureq everybody ~killed in the art expected that the monocarbinols ~nd bi~carbinols undergo substantial de~ydration since it is ganerally known from tertiary benzyl alcohols that they eliminate water when simply heated to elevated temperature~. This property o~ dehy-dration i~ even utilized in a proces ~or the production o~ un-saturated compounds, for example according to one method cited ~; in Organic Synthesis Coll~ Vol. III9 page 353, high yield3 of ~; unsaturated compounds are obtained by such elimlnation of water at temperature~ o~ from 195 to 220C. O~hydroxycymenes which

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are similar in structure ~o monocarbinols will even undergo quan-titatlve dehydration at temperatures of only about 180C (J. of Am. Chem. Soc. 71, 1367 (1949)).
According to theoretical considerations, the elimination o~ water from tertiary benzy-l alcohol~ proceeds more readily the higher the positive inductive effect of the second substituent on the aromatic ring is. Since this e~fect is more pronounced by an isopropyl group than by a methyl group (H.A. Staab, Ein~ihrung in die theor. org. Chemie, p. 594), monocarbinols and biscarbi-nols would be expected to be even more unstable than d~hydroxy-cymenes which already eliminate water quite readily (J. o~ Am.
; Chem. Soc. 71, 13677 (1949)).
But even very slight elimination o~ water during the distil-; lation o~ monocarbinols and biscarbinols has serious consequen-

3 15 ces since it reduces the yield and resulting unsaturated com-i- pounds readily polymerise and stick to the distillation appara-,~ tus a~ter a short time and i~ oxygen is present, even only in traces9 these unsaturated compounds give rise to carbonyl com-pounds which considerabl~ reduce the quality of the secondary products produced ~rom the carbinols9 for example the resol re-SinB. Moreover9 the ole~ins are virtually impossible to separate from the unreacted hydrocarbons owing to their ~ery similar phy-sioal properties and th~re~ore return with them to the oxidation ; process. ~nder the conditions prevailing in the oxidation process, 25~ they are converted into carbonyl compounds, coloured and oxida-tion-inhibitlng substances and resins. These by-products not only~directl~ reduce the yield, but also give ri~e to ~urther deoomposition reactions including the eliminatlon o~ water and reBini~ication in the course o~ distillation. Thus9 even small ~ quantities o~ ole~ins ultimately develop intens~ ef~ects. Th~y :;::

3L~16~L5;~6 must therefore not be allowed to be formed under any circumstances.
According to British Patent: No. 681,990, tertiary benzyl alco-hols may be distilled at or below a temperature of 120C. In the present case, however, this would require a vacuum of less than 1 Torr. Such medium ; high vacuum installations would be prohibitive in practice on account of their high investment and servicing costs. Moreover, even under the mild conditions mentioned in the aforesaid British Patent Specification one cannot exclude the possibility that water is eliminated since the composition of the distillates was only very inaccurately determined. In accordance with the above-mentioned British Patent Specification, therefore, the difficult separation o~ mono-carbinols and biscarbinols is carried out under the mild conditions of steam distillation with the addition of sodium hydroxide as stabilizer. However, -owing to the high consumption of steam this method is impracticable on eco-ii nomic grounds, particularly since there is the added expense which arises ~rom the fact that sodium hydroxide collects in the biscarbinol which is left as .,J
residue, so that an additional purification step is required.
It was therefore suxprising to find that monocarbinols and bis-carbinols could be separated from mixtur~ obtained from ~lkali ca~alysed ~; atmospheric oxidation of diisopropylbenzen~s by fractional distillation at 20~ pressures o at least 1 Torr and temperatures of at least 120C and purified.
The present invention therefore provides a process for the pre-paration of a substantially pure a~ tetramethyl-phenylene biscar-binol by oxidation o diisopropylhenzene in the presence o strong alkali at an ulevated temperature, wherein the reaction mixture is ~reed from the alkali by washing with water,any unreacted diisopropylbenzene is distilled off under I a pressure of rom S to 200 Torr and a~ a temperature o~ ~rom 100 to 180C, the ~onocarbinols present in th~ reaction mixture are distilled of~ under a pre~sure oP fram 10 to 100 Torr and at a temperature o from 120 to 200C, and the , a, ', a'-tetramethyl~phenylene biscarbinol is isolated by fractional distillation at a pressure of ~rom 1 to 760 Torr and at a temperature of from 120C to 280C.

~ -4-~6~5Z6 The process accordlng to the present invention is distinguished from the prior art by the simple and economical mode of operation. It may be carried out continuously or batch-wise. ][f the process is carried out batch-wise, unreacted diisopropylbenzenes are generally distilled off under a vacuum of from 5 to 200 Torr and at sump tempera1ures of from lO0 to 180C, prefer-ably from 20 to 70 Torr at temperatures oi from 135 to 165C, monocarbinols are distilled under a vacw m of from lO to lO0 ~orr and at temperatures of from 120 to 200C, preferably from 15 to 70 Torr at from 140 to 180C, and the biscarbinols are finally distilled under a pressure of from l to 760 Torr at from 120 to 280C, preferably from 5 to 70 Torr at from 150 to 205C and most preferably from lO to 50 Torr at from 165 ~o 190C.
In ~he continuous process, distillation at the above mentioned conditions may be carried out in three thin layer evaporators arranged in series in which the second evaporator, used for the separation of monocarbin-ols and biscarbinols, is normally equipped with a fractionating attachment.
If exceptionally pure products are required, the two other evaporators may also be equipped with such attachments. The distillation conditions are ~ i similar to thos~ employed for the batch-wise embodiment of the present process.

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Oxida~ion o~ the ~ opropylbenze~e~ with Rir or oxygen i~ carried out in the presencs o~ ~trong alkalie~, option-ally in the ~orm oi aqueou~ ~olution~. Oxidation i~ preter-ably carried out with ~ con¢entration of mono¢~rbi~ols ~nd/or bi~carbi~ols of at least 52%, by weight~ ln the organie pha~e and with a concentr~tion Or Alkalies oi at lea~t 8%, by weight9 ba~ed on the aqueous phase, and rrom 1 to 10%, by weight, ba~ed on the organic phase~
Suiteble ~tarting compounds ~or the pre~ent proce~s ~nclude m and p-diisopropylbenzene, ~-hydroxy-m- and a-hydroxy-diisopropylbenzene And mi~tures of the~e compou~ds~
Distillation ~raction~ which are obtai~ed ~ro~ the propyla- -tion o~ ben~ene a~d which i~ addition to at lea~t 50% by ~ : weight, pre~erably 75%, by weight, o~ dii~opropylbenzene ~ .
:~ 15 ~lso contain other propylation product~ or by-produ¢ts, such a~ cumene, trinethylindaneg phenylhexa~e or phe~ylbutane, are al~o ~ultable.
~: Suitable alkalies are ~odiu~ hydroxide a~d pota~ium hydroxide .
~ The oxidation temperature should generall~7~ be ~rom 75 ,~ to 145C and i8 prererably ~rom 90 to 120C. O~idation ~ pre~erably carried out under a pressure o~ ~rom 1 to 50 ,:
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2.2 m3 of a reaction mixture consi~ting o~: 6 % of m- and p-diisopropylbenzene, 41 % o~ m- and p~monocarbinol and 52 % of m~ and p-biscarbinol are disti:Lled in a 5 m3 still provided with a column of filling bodies. The re~lux ratio is 3 : 1.
The sump temperature becomes established at a temperature of from 140 to 150C at a pres~2ure of 20 mm Hg as long as diiso-propylbenzenes are being distilled of~. While the ~acuum i8 kept ` constant, the sump temperature is subsequently raised to 182C
for removal of the monocarbinol. Therea~ter, the ~ump temperature is raised to 200C to distil the biscarbinol o~. The sump pres-sure at this stage is ~rom 55 to 58 Torr. The residue amounts are o~ about 2.6 % b~ weight, based on the f~uantity of bi~carbi-nol put into the proces~. During the distillation o~ biscarbinol, the oondenser must be maintained at from 130 to 150C to pre~en~
f~ crystallisatlon of the compound.
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: Diisopropylbe~zefne con~i~ting o~ approximately 60g oi the m-isomer and 40% o~ the ~-ixomer i3 continuously oxidlzed with air to bi~c~rbinol in a pres~ure rea¢tor whioh i~ equipped with a hollow axial gasl~icatlon stirrer~
The~temperature i~ 100C and the pr~sure 20 bar, he NaOH oo~centratio~ is ~aint~ined at 9%~ by weight~
in the ~queou~ ph~e~ corre~po~ding to 1.5~ by weight9 ba~ed on the organic pha~g.
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The oxidate continuously di~oharged irom the reactor i8 wa6hed with water to $ree it from alkali at a temperature of ~ro~ 90 to 130C in an e~tractlo~ ~pp~r~tus~ The puriiied oxid~te i8 then oo~tinuou31y ~ed lnto a di~tillatlo~ plant 39 coneletin~ oi the ~ollowing p~rt~:

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~4S~26 l~e apparatus used for the first stage is a thin layer evaporator the sump of which enters the second stage consisting of a thin layer evaporator and short fractionating column. The sump which contains biscarbinol already sufficiently pure for numerous purposes is pumped into a third thin layer evaporator in which pure biscarbinol is distilled off. l~e distillation conditions employed and analytical data are summarized in the following Tahle.

Experiment Supply Distillate Residue Temperature Pressure ~i~
No. sump ~leadSump Head '~ ~!
kg/h kg/h kg/h C C Torr Torr 1st Stage . . .
1 283.9 - 150 40 , 2 283.4 - 160 70 2nd Stage 1 11 12.7 183 125 28 15 2 12 12.1 183 122 29 15 3rd Stage ,.1~ ,, -~ 1 12.1 0.5 180-3 26-27 j ~: :
2 11.8 0.3 195-200 51-55 The starting material, distillates and residue are analyzed by means of gas chromatography: j' Starting 1st Stage 2nd Stiage 3rd Stage material Distillate Distillate Residue Distillate ---~ % % _ % % % '`
Diisopropyl-benzene 7.3 45.0 8.5 Monocarbinol46.7 48.9 91.4 0.5 below 0.2 Biscarbinol 46.0 6.1 0.1 ~99 ~99.8 ~ b) The biscarbinol residu0 ~rom the second distillation stage is condensed with phenol as ~ollows:
A mixture of 194 g biscarbinol Cl mol)~ 752 g ~ : :

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( 8 mol ) of phenol and 10 ml of 85% phosphoric ~aid iB
heated to a reaction tempera-ture of 80C with stirring at re~uced pressure while the water produced by the re~otion i8 distilled of~. After a reaction time of 2 hour~, the water is removed and a pressure of 25 Torr is reached~
After a further 6 hours, 8.8 ml of concentrated sodium hydroxide solution are ~dded and the phenol i~ distilled o~
at tempaxatures of up to 210C and 10 Torr. 278 g of a clear5 pale hard resin with a phenolic OH content of 7.5 and a colour number of O are obtained.
~he colour number iq taken irom the iodine scale a~d determined on a 50% solution of the resln in n-butanol.
~, (c) 200 g of 30% fo~alin are added to a solutio~
which is ~t a p~ of from 8 to 9 o~ 278 g o~ the condensation 15 ~ resin obtained according to ~b) in 556 g o~ but~nol~ and ~i`; the mlxture is heated to a temperature of ~rom 91 to 93C for <~ 8 hours. Aiter the additio~ o~ 200 g o~ water9 the p~ is ' adju~te~ to 4 with a ~ew drops o~ phosphoric ~cid to improve : pha~e separatlon and the lower (aqueous) phase i8 removed ~;; 20~: at~600C. After ~eparatio~ o~ the pha~es at 600~, the organio phBBe iS dehydrated azeotropically, conoentrated to the required solld:content by e~apor~tio~ and filteredO
: ~ Yield: 530 g Or 60% resol resln i~ butanol.
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A~ter the addition o~ 0.5% of a 10% ~3PO~ and 3~ of a~ etheri~ied melamine~ormaldehyde resin (Maprenal NP ~ ), ~` the resol resin i~ ~i~e~ with an equal qua~ltity o~ epoxlde : resi~ 1007 (Shell)a applied to metal sheets a~d stoved at 18ûC îor 12 minute~. A colourles~, exception~lly chemlcally resistant coating which iB st0rili~able and capable o:~ being o ~ deep drawn is obtaille~l.

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of a substantially pure .alpha., .alpha., .alpha.' .alpha.'-tetramethyl-phenylene biscarbinol by oxidation of diisopropylbenzene in the presence of strong alkali at an elevated temperature, wherein the reaction mixture is freed from the alkali by washing with water,any unreacted diiso-propylbenzene is distilled off under a pressure of from 5 to 200 Torr and at a temperature of from 100 to 180°C, the monocarbinols present in the reaction mixture are distilled off under a pressure of from 10 to 100 Torr and at a temperature of from 120 to 200°C, and the .alpha., .alpha., .alpha.', .alpha.'-tetramethyl-phenylene biscarbinol is isolated by fractional distillation at a pressure of from 1 to 760 Torr and at a temperature of from 120°C to 280°C.

2. A process as claimed in Claim 1, wherein unreacted diisopropyl-benzene is distilled off under a pressure of from 20 to 70 Torr and at a temperature of from 135 to 165°C.

3. A process as claimed in Claim 1, wherein the monocarbinols are distilled off under a pressure of from 15 to 70 Torr and at a temperature of from 140 to 180°C.

4. A process as claimed in Claim 1, 2 or 3, wherein the biscar-binols are distilled off under a pressure of from 5 to 70 Torr and at a temperature of from 150 to 205°C.

5. A process as claimed in Claim 1, 2 or 3, wherein the biscar-binols are distilled off under a pressure of from 10 to 50 Torr and at a temperature of from 165 to 190°C.