DE2736948C3 - Process for the preparation of a monovinylidene aromatic monomer by dehydration - Google Patents

Description

10

15th

in which R is hydrogen, an alkyl radical with 1 to 12 carbon atoms or halogen and Ri is hydrogen or an alkyl radical with 1 to 4 carbon atoms, at a temperature of 200 to 510 ^° C. in the presence of 0.03 to 25 parts by weight of added water 1 part by weight of alcohol and in the presence of a silica as the dehydration catalyst, characterized in that the dehydration catalyst used is finely divided silica gel with a surface area of at least 300 mVg.

2. The method according to claim I _1, characterized in that the silica gel has an average pore diameter in the range from 0.2 to 20 nm

35

This invention relates to a process for the preparation of a monovinylidene aromatic monomer such as Styrene or a substituted styrene by dehydrating an α-methylbenzyl alcohol or a «-Alkyl-substituted methylbenzyl alcohol.

The dehydration of alcohols to the corresponding unsaturated compounds is known However, dehydration processes are generally not used for the manufacture of styrene and its used numerous homologues, since the usual dehydrogenation of ethylbenzene than the more economical Route is viewed. In addition, styrenes produced by conventional dehydration processes often contain interfering amounts of ethylbenzene and of other contaminants so that thorough cleaning is required

It is characteristic of the usual dehydrogenation processes for the production of styrene that quite large amounts of unreacted ethylbenzene in the Styrene fraction are present. Such amounts of ethylbenzene in the styrene fraction can be so high be that they impair the properties of the polymers from such styrene fractions. Because of the The proximity of the boiling points of styrene and ethylbenzene is ω In addition, the removal of the ethylbenzene by distillation is costly.

In addition, the normal dehydrogenation of numerous substituted ethylbenzenes, in particular the tertiary alkyl-substituted ethylbenzenes, the «5 substituted group destroys or changes The dehydrogenation of ar (t-alkyl) -äthyIbenzol to the corresponding styrenes usually leads to a Breaking up and / or loss of the t-alkyl group and for Dehydration of the ethyl group. Under the prefix "ar" it is to be understood that the aromatic compound in question is substituted on an aromatic nucleus is, various positional isomers are possible.

Attempts to produce ar- (t) alkyl) styrenes by usual dehydration of the corresponding ar- {t-alkyl) - «- methylbenzyIalkohoIe do not have led to a satisfactory result, since other by-products are formed and the dehydration is also often accompanied by breakdown of the t-alkyl group as a result of this breakdown there are significant amounts of ethylbenzene and, under certain conditions, diolefinically unsaturated aromatic monomers are also added the desired ar- (t-alkyI) styrene formed These diolefinically unsaturated aromatic monomers, z. B. ar- (isopropenyl) styrene during dehydration of ar- (t-butyl) - «- methylbenzyl alcohol, are very difficult of the desired ar- (t-alkyl) styrGl to separate. During the polymerization of the ar- (t-alkyl) styrene monomer, the diolefinically unsaturated aromatic monomer acts as a cross-linking agent, whereby a substantially crosslinked styrene polymer is formed which is insoluble in numerous organic solvents such as toluene and benzene Lack of solubility is undesirable for some applications of such styrene polymers

Customary dehydration processes are not used for the production of styrene and substituted styrenes completely satisfactory, since there are significant amounts of ethylbenzene and others in the reaction product difficult to separate impurities remain or are generated. Such difficulties are for example, in US Pat. Nos. 2,399,395 and 3,442,963.

It would therefore be very desirable to find a new improved process for the production of styrene and To have substituted styrenes available, in which these products in high yield and with little or no Ethyibenzene and other impurities, especially diolefinically unsaturated aromatic Monomers are obtained.

The invention provides such an improved process for the dehydration of α-methylbenzyl alcohols and for producing the corresponding styrene monomers in high yield and high purity for Disposal.

The invention therefore relates to a process for the preparation of an aromatic monovinylidene monomer by dehydrating an α-alkylbenzyl alcohol of the general formula

in which R is hydrogen, an alkyl radical with 1 to 12 carbon atoms or halogen and Ri is hydrogen or an alkyl radical with 1 to 4 carbon atoms, at a temperature of 200 to 510 ^° C. in the presence of 0.03 to 25 parts by weight of added water 1 part by weight of alcohol and in the presence of a silica as a dehydrating agent

catalyst, this process being characterized in that it is used as a debydration catalyst finely divided Siükagel with a surface area of at least 300 mVg is used

In the method according to the invention, a type of silica gel is used as the dehydration catalyst, which has previously served as a support for other catalysts. It has surprisingly been found that this type of silica gel under the specified process conditions compared to known catalysts ι ο The yield of the desired styrene is significantly increased and the formation of ethylbenzene and others is difficult removing impurities is significantly reduced and, under optimal conditions, almost completely In general, the desired monovinylidene aromatic monomer is greater in size Obtained and contains purity as about 99 mole percent less than about 1, preferably less than about 0.5 mole percent alkylbenzene impurity, also known as Ethylbenzene contamination can be referred to. A particular advantage of the method according to the Invention is that when it is used for the production of ar- (t-alkyl) -styrenes, the sensitive t-alkyl radicals remain unchanged, so that in in this case products of high purity can be obtained.

In DE-OS 21 46 919, the production of styrene by elimination of water from «-Methylbenzylalkohol in described the gas phase at a temperature above 260 ° C in the presence of an oxide catalyst, with 0.1 to 4 moles of water vapor being added per mole of organic feed. Ak, oxide catalyst As a rule, aluminum oxide is used, but kierjl acid is also mentioned among the oxide catalysts without further details being given. Alumina has proven to be a catalyst among the Process conditions of the present invention not proven and from the large group of under the Substances falling under the designation "silica" result only in the silica gels used according to the invention desired monomers in high yields and high purity

From SU-PS 3 89 069 it is known to obtain styrene by catalytic dehydration of α-methylbenzyl alcohol in the presence of steam, but this patent specification is also not a teaching for the use of the in the present invention used silica gel catalyst to be taken.

It follows from this that sryrole monomers produced according to the invention are only smaller or even lower Do not require further cleaning to remove impurities that have boiling points near the Boiling point of the monomer. This eliminates the need for complex distillation processes. Styrene polymers, the made from these styrene monomers have improved properties as a result of higher purity of the monomers. Since the monomers are low concentrations, especially less than 0.02 mol%, based on the total monomer, of diolefinic impurities can contain ar- (t-alkyl) styrenes obtained according to the invention are converted directly to polymers which are in toluene, benzene and other organic solvents are soluble. Such polymers which are soluble in organic solvents are particularly suitable as coating compositions and thermoplastic molding compositions; the monomers can can also be used as reactive diluents in polyester resin paints and other chemical applications that contain a monomer require the int to be substantially free of diolefinic compounds

For the methylbenzyl alcohols used as starting materials and characterized by a formula R can be hydrogen, an alkyl radical having 1 to 12 carbon atoms, e.g. B, a methyl, t-butyl, t-amyl or another t-alkyl radical; Halogen, e.g. B. bromine, chlorine or fluorine and R) hydrogen or an alkyl radical with 1 to 4 carbon atoms.

Examples of «x-MethylbenzylalkohoIen are

a-methylbenzyl alcohol,

ar-chloro-Ä-methylbenzyl alcohol,

ar-bromo-ot-methylbenzyl alcohol,

ar-fluoro-a-methylbenzyl alcohol,

ar-dichloro-a-methylbenzyl alcohol,

ar-dibromo-ar-cWor-a-methylbenzyl alcohol,

ar-chloro-a-ethylbenzyl alcohol,

4-ChloΓ-2 £ -difluoro - «- methylbenzyl alcohol,

ar- (t-butyl) - «- methylbenzyl alcohol,

ar- (t-amyl) - «- methylbenzyl alcohol,

ar-a-dimethylbenzyl alcohol,

ce-ethyl ^ -isopropyl-S-methylbenzyl-

alcohol or oc-Isobutyl ^ AS-triraethylbenzyl alcohol.

Preferred α-methylbenzyl alcohols are α-methylbenzyl alcohol, ar-halogen - «- methylbenzyl alcohols such as ar-chloro and ar-bromo-Ä-methylbenzyl alcohol and ar- (t-alkyl) - «- methylbenzyl alcohol such as p- (t-butyl) -« - methylbenzyl alcohol, p- (t-amyl) - <x-methylbenzyl alcohol and similar alcohols in which the t-alkyl radical is 4 Contains up to 8 carbon atoms These alcohols are known compounds and can be separated by known or analogous processes which are readily available to the person skilled in the art. So you can for example ar-alkyl-a-methylbenzyl alcohol obtained a multi-step synthesis by 1. ethylbenzene with an olefin in the presence of Sulfuric acid according to the method of Ipatieff et al., JACS, Vol. 58, 919 (1936), alkylated, 2. the alkylated Ethylbenzene to the corresponding acetophenone alcohol mixture according to H. J. Sanders et al, 1 & E Chem., Vol. 45, 2 (1953), and 3. the mixture is oxidized by catalytic hydrogenation to give the desired alcohol reduced

The silica gel used in the invention can be used in be of any form that allows intimate contact between the silica gel and the alcohol vapor allows during dehydration. Preferably, the silica gel should be in the form of a finely divided Solid are present, the particles of which, in particular, do not have a larger extension than approximately in any dimension Should be 2.5 cm. In addition, the silica gel should be such that when it comes into contact with larger Amount of water is not degraded or destroyed. The best results will be with silica gel with a Maintained surface of 300 to 900 mVg. Commercially available silica gels previously known as Supports for other catalysts have been used. Finely divided, porous ones have proven particularly useful Silica gels with an average pore diameter of 0.2 to 20 nm. Process for the production of such Silica gels are well known in the art. It is also possible to use some of the commercially available silica gels that the correspond to the above characterization.

In practicing the invention, will the «-Alkylbenzyl alcohol in the vapor phase with the Silica gel in the presence of 0.03 to 25 parts by weight Water per part by weight of alcohol, preferably 0.5 to 20 parts by weight, in particular 1 to 2 parts by weight Water per part by weight of alcohol contacted. In general, it is preferred that the Alcohol with the specified amount of water in the form of steam before dehydration intimately is mixed. This is achieved in a simple way, by flowing liquid or vapor mixtures of alcohol and water over or through a bed or a column with an effective heat transfer material such as silicon carbide, fused ceramic packings or non-corrodible metal packages conducts. In such embodiments, one can use a Use a column that has a lower part with a bed of silica gel and an upper part with the heat transfer medium contains, with the hydrous alcohol down in the column through the heat transfer medium and then passed through the silica gel bed. It is often desirable to use a liquid organic carrier to be used, which is a solvent for the alcohol, e.g. B. toluene or benzene, this carrier so should be selected so that it can be removed by simple distillation. In such embodiments the alcohol and the liquid carrier prior to evaporation of the alcohol mixture mixed It is also possible in the invention for the water to be added to the alcohol first After the alcohol has passed through Jas heat transfer medium, there is also no need add the water in the form of steam or superheated steam, although this is preferred

In the invention, the process temperatures are from 200 to 51O ⁰ C, preferably 260-500 ⁰ C, in particular 300 to 400 ⁰ C. In the dehydration of ar- (t-alkyl) - «- methylbenzylalkohoIen it is desirable dehydration temperatures above 260 ° C, especially 325 to 425 ° C, to ensure contact between the silica gel and the alcohol in the vapor phase. In general, it is desirable to carry out the dehydration at atmospheric pressure, although it is also possible to carry out dehydration with relatively good purity and yield at sub-atmospheric or super-atmospheric pressure, for example 0.2 to 5 atmospheres. The evaporation of the alcohol can be achieved with advantage, however, by using reduced pressure. Evaporation can also be achieved by contacting the alcohol with steam or superheated steam substantially prior to dehydration.

The required amount of silica gel that leads to effective dehydration of the alcohol depends on in part on the rate at which the vaporous alcohol passes through the bed or column of the silica gel, the surface area of the gel per unit weight and the amount of added Water. In general, higher steam speeds and larger amounts of water are required more silica gel to induce effective dehydration.

As has already been stated, in the invention the desired aromatic monovinylidene monomer, in particular ar- (t-alkyl) styrene in a purity> on higher than 99 mol-V. based on the total product, obtained after a simple distillation in which unreacted ketones and alcohols are removed. This makes the alkylbenzene impurity below about 1 mole percent, preferably below about 0.5 Mole% held. In the dehydration of the ar- (t-AI-kyl) -a-methylbenzyl alcohols by the method according to the invention, the proportion of diolefinic and other polyolefinic impurities below 0.02 mol%, based on the total product a simple distillation.

The invention is explained in more detail in the following examples. All data relating to parts and percentages are weights unless otherwise specified.

example 1

A first mixture of 50 parts of "methyl benzyl alcohol and 50 parts of toluene is preheated to 300 ⁰ C and mixed with 100 parts of water vapor at 300 ⁰ C The water vapor ZAlkohoImischung obtained was passed down at a rate corresponding to that of Example 2 through a glass column (outer diameter 2 cm, length 69 cm), which is equipped with an electric furnace of an upper layer of 36 cm silicon carbide (particle size 232 mm), heated to 350 ^° C., and a lower 15 cm layer (20 g ) of silica gel (particle size 1.68 mm) surface 30Om ² / g and pore volume 1 ccm / g has water and dehydrated organic product are condensed and separated in the lower part of the column The organic product is dried and distilled The distilled product is determined by infrared spectroscopy and vapor phase chromatography found to contain 99+ mole percent styrene and less than 0.5 mole percent ethylbenzene Today based on alcohol is greater than 95%.

Example 2

A mixture of 50 parts of 4- (t-butyl) - «- methylbenzyl alcohol and 50 parts of toluene is prepared. A reaction column with an outer diameter of 2.5 cm and a length of 62 cm is used up to a bed height of 203 to 223 cm Silica gel (particle size 1.68-2 ^ 8 mm), surface 34OmVg, 14 nm mean pore diameter and a sufficient amount of silicon carbide (particle size 3.36 mm) to fill the tube up to a total height of 41 cm. The reaction column is heated to 300 ⁰ C. Preheated to 300 ⁰ C of water and the mixture are at the same time the feed end of the column at rates of 90 ml / h and 45 ml / h supplied Fi is produced an intimate mixture of water vapor and alcohol in the vapor phase, the down over the 350 ⁰ C Preheated silicon carbide reddish, which acts as a preheating zone for the steam.Then the mixture passes through the silica gel, where dehydration occurs.After passing through the silica gel, Walser and organic product are condensed and collected in the column.The dehydrated organic product is decanted, dried and distilled The distilled product is examined by infrared spectroscopy and vapor phase chromatography, and it is found that 4- (t-butyl) styrene is obtained in a purity of 99% or greater. The overall yield based on the alcohol used is greater than 90%.

During the polymerization of 4- (t-ButvI) stvrols through

Heating in the presence of benzoyl peroxide produces a polymer which is soluble ^{in toluene at 20 ° C.}

Example 3

Some experiments in accordance with the procedure of Example 2 are carried out. In these experiments, mixtures of 50 parts of 4- (t-butyl) - <* - methylbenzyl alcohol and 50 parts of toluene are Herge and mixed with different amounts of steam. The vaporous mixture of water and alcohol is passed down into a glass column (outer diameter 2.5 cm, length 69 cm). The column has an upper bed of silicon carbide (1.68 mm) 36 cm high, which is preheated to different temperatures, and a lower bed of silica gel (the same as in the example of Ptnpr Möhp vnn üfm Am RrvHpn Apr Κrtlnnnt * ) and the dehydrated organic product condensed, collected and separated as in Example 2. The results are summarized in Table I.

To demonstrate the particular advantages of adding water to this system, a comparative experiment (Ci) was carried out under conditions similar to the experiments of the invention, except that no water was added to the alcohol at any time before or during dehydration became. The results of this control experiment are also given in Table I. In order to determine the upper limits for the temperature during dehydration, two control tests (Cj and Ci) were carried out using different amounts of water according to the same procedure. These results are also shown in Table I ηιιΓπρηηπιηιρη

le I SV. ^ Ser / alcohol Re.iklions- ^e Polymer dissolving soluble Tdbel ■ h no temperature ¹ ' 4- (t-Bmyhiithylhen / ol ^hchke "' soluble \ ίΜΗ Tetle / right left " ^C \ 'pollution "I Mol- '. soluble 5.0 410 hopropenylstyrene 0.15 soluble ■ 1.4 406 Mol- ¹ . 0.15 soluble 1 0.84 406 0 0.14 soluble --0.5ft 395 0 0.13 soluble . ' 20.0 393 0 0.2 soluble 4th -20.0 445 0 0.2 soluble 5 - 20.0 505 0 0.7 soluble ft * 0.50 400 0 0.1 insoluble - -0.50 448 <0.02 0.4 insoluble --0.50 506 0 0.6 insoluble '■> -0 400 0 0.23 ld --20.0 550 <0.02 1.4 silicon carbide used as a heat transfer medium C * ι • 0.50 550 0.12 1.5 In mole of the n- (t-butylistrols produced: determined by gas phase (/; *! n: ei of the birth > 0.11 C -. 'I p. At-i .on = temperjlur entv prichl the temperature of the > 0.18 '· Kei R. \ ik; • | Respected ^ * ninr-2> rveiini> ■ D: -

raphy and infrared spectroscopy
'.on Hi pu-But>l>st> Tolpolyme-: m in toluene at 23 ⁼ C.

In accordance with the continuous dehydration procedure of this example, some substituted α-methylbenzyl alcohols are dehydrated to the corresponding substituted styrenes. The results are comparable to those of this example. The following alcohols were dehydrated:

ar-t-Butyl- * jx-dimethylbenzyl alcohol, ar-dichloro-a-methylbenzyl alcohol, ar-dibromo - * - methylbenzyl alcohol, ar-di-t-butyl-a-methylbenzyl alcohol, ar- {I -ethyl-1-methylpentyl) - <x-methyl-

benzyl alcohol, ar-t-Butyl-ar-methyl-a-methylbenzyl alcohol

Some experiments were also carried out with good results using a silica gel catalyst of various particle sizes or mesh sizes and surfaces in the range from 300 to 900 mVg.

60

Example 4

Some experiments were carried out essentially as in Example 2, with the exception that the Temperature was varied within a wide range. The various attempts were made Mixtures of 50 parts of ar- (t-butyl) - «- methylbenzyl alcohol, about 7 mol% of ar- {t-butyl) acetophenone and 50 parts of toluene. A glass column (outer diameter 2.5 cm, length 41 cm), which was equipped with an electric furnace, which was filled with silicon carbide up to a height of 8.9 cm (Particle size 2.38 cm, 42 g) a total height of ^ Mr ^ M ~ Liu ItKi uuuuigvt ^ uuä givivitv ni \. »I **%, ta | s ™ .i A ^ .sw gs and a total height of 41 cm with silicon carbide (Particle size 2.38 mm, 40 g) was filled with the various attempts at temperatures from 200 to

ίο

500 ^c C. Steam superheated to at least 550 ° C. and the alcohol / toluene mixture were simultaneously fed to the feed end of the column at rates of 100 ml / h (measured as condensed water) and 50 ml / h, respectively. An intimate mixture of water vapor and the alcohol mixture was formed in the vapor phase which was passed down through the heat transfer medium and silica gel to cause dehydration. The water and organic product were then condensed, collected and separated. The organic product was distilled and dried. Its components were determined by infrared spectroscopy and vapor phase chromatography. The results are shown in Table II. As opposed to the advantages of the silica gel catalyst

Table Il

To show conventional dehydration catalysts, some comparative experiments (04-Cs) were carried out in which essentially the same procedure was used, with the exception that a titanium dioxide dehydration catalyst (particle size 1.68-4.76 mm, surface area 70 mVg) was used in place of silica gel. The dehydration column had a bottom layer of 8.9 cm of silicon carbide (particle size 2.38 mm), a 25.4 cm middle layer of titanium dioxide catalyst and a 6.4 cm top layer of silicon carbide. The organic product was isolated and analyzed by infrared spectroscopy and vapor phase chromatography. The results obtained by infrared spectroscopy and vapor phase chromatography are given in Table II.

Sample no.

Reaction temperature

Catalyst product composition. Mol- ""

ar-d-Butyh- iir- (t-Butyl) - ar- (t-Butyl) - ar- (t-Bulyl) - <7-methyl-

styrene ethylbenzene acetophenone benzyl alcohol

I. 250 ° Silica gel 92.1 0.5 4.4 2 350 ° Silica gel 95.3 0.3 4.5 3 350 ° Silica gel 95.9 0.3 3.9 4th 400 ° Silica gel 97.2 0.2 2.6 5 450 ° Silica gel 95.3 0.2 4.5 6th 500 ° Silica gel 94.2 0.5 5.3 C ₄ *) 250 ° anhydrous
Titanium dioxide 97.3 0.4 2.3 C ₅ *) 300 ° anhydrous
Titanium dioxide 97.2 0.6 2.2 C ₆ *) 350 ° anhydrous
Titanium dioxide 94.1 1.9 4.0 C ₇ *) 400 ° anhydrous
Titanium dioxide 91.9 5.4 2.7 Γ * \ al ς η ι 1 I. Titanium dioxide *) None Example according to the invention.

3.0

As can be seen from Table II, substantially larger amounts of ar- (t-butyl) ethylbenzene are generally used in the dehydration with titanium dioxide formed than when using silica gel as a catalyst under essentially the same conditions.

50 The ar- (t-butyl) ethylbenzene is difficult to separate from the ar- (t-butyl) styrene, whereas ar- (t-butyl) acetophenone can be separated from both by simple distillation is detachable.

Example 5

A solution of 50 parts of ar- (t-butyl) - «- methyIbenzylaikohol, which contains about 7 mol% ar- (t-ButyI) acetophenone, in 50 parts of toluene is ^{superheated to 550 0} C steam in a ratio of 2 Parts of water mixed with part of the mixture. The steam-alcohol mixture is passed downward through a glass column with an outer diameter of 2J5 cm and a length of 53 cm. The column contains an upper layer of silicon carbide of 25.4 cn! and a 25.4 cm lower layer of the same silica gel as in Betspiel 2. The temperature at the top of the column is 350 ° C. and at the bottom 325 ° C. The water and the organic product are distilled and dried Its components are through Infrared spectroscopy and vapor phase chromatography determined. The results are in Table III compiled

For comparison purposes, a comparative experiment (C9) is carried out under the same conditions, with the exception that aluminum oxide (particle size 1.68-4.76 mmX surface area 210m ² / g is used as the dehydration catalyst instead of silica gel

approx . The organic product is distilled and dried. The results are also given in Table III

Il

Table III

Try the catalyst No.

Product composition, mol% P- (I-BuIyI) - m- (t-butyl) - ar- (t-butyl) -

slyrol

styrene

ethylbenzene ar- (t-butyl) -toluene and ar- (t-butyl) benzene

ar- (t-butyl (acetophenone ar- (t-butyl) -ff-methylbenzyl alcohol, ppm

Silica gel

96.09

Alumina 96.52

*) No example according to the invention.

3.77
2.32

0.10 1.08 0.04
0.08

<25 ppm
~ 45 ppm

Example 6

The dehydration process of the present invention is carried out in a continuous manner by ar- (t-Hutyi) continuously molten - «- methylbenzyl h in an amount of 90.7 kg / and superheated to 550 ⁰ C water in an amount of 181.4 kg / h of a column with an outer diameter of 46 cm and a length of 2 m. The column contains an upper bed of metallic transition material with a height of 1 m, which ^{is heated to 350 °} C., and a lower bed with a height of 1 m made of the same silica gel as in Example 2. The temperature at the lower end of the column is 325 ° C. The dehydrated organic product is continuously collected at the lower end of the column and worked up by simple distillation with a purity of 99 ^{+ o} / o. The dehydrated product is identified as ar- (t-butyl) styrene by infrared spectroscopy.

Example 7

Some samples of ar-chloro-oc-methylbenzyl alcohol, which contain small amounts of ar-chloro-acetophenone, are continuously dehydrated by mixing the liquid alcohol with different amounts of superheated steam (55O ⁰ C) and in the vapor phase through the Column of Example 3 leads. The dehydration temperatures for the different experiments are also varied. The amounts of the low

2ϊ boiling components can be seen from Table IV. For comparison purposes, similar samples of ar-chloro-at-methylbenzyl alcohol, which were also low Amounts of ar-chloro-acetophenone contained, continuously dehydrated in the same way with the

jo exception that no water was added. the Amounts of the low-boiling components in these comparative tests (Cio, Cn, C12) are given in Table IV also indicated.

Tabel IV Reaction
temperature Low boiling
mixture. Part ¹ Components
) the reaction Low boiling
Impurities /
ar-chlorostyrene Sample no . Water / alcohol ⁰ C ar-chlorine-
styrene ar-chlorine-
ethylbenzene other I hurry / 1 (X) leile ml / 100 ml 400 62.89 1.10 0.22 2.1 1 3 400 76.19 0.88 0.19 1.4 2 5 400 55.80 1.88 0.45 4.2 C ₁₀ *) 0 350 73.91 0.16 0.09 0.34 3 25th 350 58.90 0.89 0.27 1.80 C ₁₁ *) 0 400 78.11 0.03 NB **) 0.04 5 50 400 63.64 1.61 0.45 3.23 C ₁₂ *) 0

*) No example according to the invention. **) Not determined

') Higher-boiling components including chloroacetophenone and ar-chloro-c-methylbenzyl alcohol form the remainder Reaction mixture, which consists of a total of 100 parts.

Example 8

"- - according to the general procedure of Example 1, 4 different alkyl methyibenzyIalkohole be blended with toluene and passed through a heated dehydration this column has as a heat exchanger mm a silicon carbide having a particle size of 238 to 350 ⁰ C.

65 is preheated and underneath a layer of silica gel with a particle size of 1.68 mm and a surface of 300 mVg.

The reaction products are xennt in any case g ^ and worked to obtain the desired styrene homologs. The starting alcohols and the corresponding styrene homologues are given below:

alcohol

t-amyl methyl benzyl alcohol

t-hexyl methylbenzyl alcohol

t-octyl methylbenzyl alcohol

t-dodecyl-m ethyl benzyl alcohol

14th

Styrene homologs

t-amyl styrene t-hexyl styrene t-methylethylpentyl-

styrene

t-dodecyl styrene

When these t-alkyl - «- methylbenzyl alcohols were dehydrated, the corresponding styrene homologue became in each case in a yield of higher than 99.5 mol%, based on the starting alcohol.

Claims (1)

Patent claims: 1. A process for producing a monovinylidene aromatic monomer by dehydration an-methylbenzyl alcohol or an -alkyl-substituted methylbenzyl alcohol of the general formula