DE2736948B2 - Process for the preparation of a monovinylidene aromatic monomer by dehydration - Google Patents

Description

OH

C - CH ₂

I I

R ₁ H

10

15th

in which R is hydrogen, an alkyl radical having 1 to 12 carbon atoms or halogen and Ri is hydrogen or an alkyl radical having 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 m ² / g

2. The method according to claim 1, characterized in that the silica gel has an average pore diameter in the range from 0.2 to 20 nm

50

This invention relates to a process for the preparation of a monovinylidene aromatic monomer such as Styrene or a substituted styrene by dehydrating a «-Methylbenzylalkohols or one «-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 numerous homologues used as the usual dehydrogenation of ethylbenzene as 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 are present in the styrene fraction. Such amounts of Ethylbenzene in the styrene fractions can be so high that they reduce the properties of the polymers affect such styrene fractions. Because of the proximity of the boiling points of styrene and ethylbenzene is 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, which destroy or change the substituted group. the Dehydrogenation of ar- (t-alkyl) ethylbenzene to the corresponding styrenes usually leads to a Breaking up and / or loss of the t-alkyl group and zor 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 customary dehydration of the corresponding ar- (t-alkyl) -a-methylbenzyl alcohols 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-alkyl) styrene formed These diolefinically unsaturated aromatic monomers, z. B. ar- (isopropenyl) styrene during dehydration of ar- (t-butyl) - <x -methylbenzyl alcohol, are very difficult of the desired ar- (t-alkyl) styrene to separate. During the polymerization of the ar- (t-AI-kyl) styrene monomer, the diolefinically unsaturated aromatic monomer acts as a crosslinking agent, with 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 ethylbenzene 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 -alkylbenzyl alcohol of the general formula

R is hydrogen, an alkyl group having 1 to 12 carbon atoms or halogen and R, is hydrogen or an alkyl group having 1 to 4 carbon atoms is added at a temperature of 200-510 ⁰ C in the presence of 0.03 to 25 Waxed parts of water to 1 part by weight of alcohol and in the presence of a silica as a dehydrating agent

catalyst, this process being characterized in that the dehydration catalyst used is finely divided silica gel with a surface area of at least 300 m ² / g

In the process of 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 die 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 becomes larger in size Obtained purity as about 99 mole percent and contains less than about 1, preferably less than about 0.5 Mole - "* alkylbenzene impurity, also known for short 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 preparation is described of styrene by dehydration of "methyl benzyl alcohol in the gas phase at a temperature above 260 ⁰ C in the presence of an oxide catalyst, wherein 0.1 to 4 moles of water vapor per mole of organic feed added . As a rule, aluminum oxide is used as the oxide catalyst, but silicic acid is also mentioned among the oxide catalysts, without further details being given. Aluminum oxide has not proven itself as a catalyst under the process conditions of the present invention and from the large group of substances falling under the designation "silica" only the silica gels used according to the invention give the desired monomers in high yields and high purity

From SU-PS 3 89 069 it is known to use styrene to win catalytic dehydration of «-Methylbenzylalkohol 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 styrene 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 the 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 that is essentially 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 Ri is hydrogen or an alkyl radical with 1 to 4 carbon atoms.

Examples of -methylbenzyl alcohols are

a-methylbenzyl alcohol,

ar-chlorine - «- methylbenzyl alcohol,

ar-bromo-a-methylbenzyl alcohol,

ar-fluoro-oc-methylbenzyl alcohol,

ar-dichloro-methylbenzyl alcohol,

ar-dibromo-ar-chloro-a-methylbenzyl alcohol,

ar-chloro-flt-ethylbenzyl alcohol,

4-Ch! Or-2,5-dtrluoro - «- methylbeiicyl alcohol,

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

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

ar-a-dimethylbenzyl alcohol,

«-Atiiyl-2-isopropyl-5-methylbenzyl-

alcohol or ot -isobutyl-2,4,5-triethylbenzyl alcohol.

Preferred ac-methylbenzyl alcohols are a-methylbenzyl alcohol, ar-halo-flc-methylbenzyl alcohol such as ar-chloro and ar-bromo-a-methylbenzyl alcohol and ar- (t-alkyl) - (x-methylbenzyl alcohol such as p- (t-butyl) - «- methylbenzyl alcohol, p- (t-amyl) - «- 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- «- methylbenzyIalkohole obtained by a multi-stage synthesis by 1. Ethylbenzene with an olefin in the presence of sulfuric acid according to the method of Ipatieff et al., JACS, VoI. 58, 919 (1936), alkylated, 2. the alkylated Ethylbenzene to the corresponding acetophenone-alcohol mixture according to H. J. Sanders et al., I & 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 in any form which allows intimate contact between the silica gel and the alcohol vapor during dehydration. The silica gel should preferably be in the form of a finely divided solid, the particles of which, in particular, should not be larger than about 2.5 cm in any dimension. In addition, the silica gel should be such that it is not broken down or destroyed on contact with large amounts of water. The best results are obtained with silica gel with a surface area of 300 to 900 m ² / g. Commercially available silica gels which have hitherto been used as supports for other catalysts are particularly preferred. Finely divided, porous silica gels with an average pore diameter of 0.2 to 20 nm have proven particularly useful. Processes for producing such silica gels are well known in the art. It is also possible to use some of the commercially available silica gels that meet the above characterization.

In practicing the invention, the «-alkylbenzyl alcohol is in the vapor phase with the Silica gel in the presence of 0.03 to 25 parts by weight of water per part by weight of alcohol, preferably 0.5 to 20 Parts by weight, in particular 1 to 2 parts by weight of water per part by weight of alcohol in contact In general, it is preferred that the alcohol with the stated amount of water in the form is intimately mixed by steam before dehydration. This is achieved in a simple manner 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 packings In such embodiments, one can use a column that has a lower section with a bed made of silica gel and an upper part containing the heat transfer agent, the hydrous alcohol is passed down the column through the heat transfer medium and then through the silica gel bed. It It is often desirable to include a liquid organic carrier that is a solvent for the alcohol is 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 Carriers mixed prior to evaporation of the alcohol mixture. It is also possible in the invention that the The water is added to the alcohol only after the alcohol is the heat transfer medium Also, there is no need to take the water in the form of steam or superheated Add steam, although this is preferred.

In the invention, the process temperatures are from 200 to 510 ⁰ C, preferably 260-500 ⁰ C, in particular 300 to 400 ⁰ C. In the dehydration of ar- (t--alkyl) - «- methyl benzylic it is desirable Dchydratisierungstemperaturen above 260 ⁰ C, in particular 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 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 water added. In general, higher steam speeds and larger amounts of water add more silica gel to effective dehydration bring about.

As has already been stated, in the invention the desired aromatic monovinylidene monomer, in particular ar- (t-alkyl) styrene in a purity of more than 99 mol%, 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-alkyl) - «- methylbenzyIalkohole by the process according to of the invention is 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 a-methyl benzyl alcohol and 50 parts of toluene is preheated to 300 ⁰ C and mixed with 100 parts of water vapor at 300 ° C The water vapor ZAlkoholmischung obtained was passed down at a rate corresponding to that of Example 2 through a glass column (outer diameter 1 $ cm, length 69 cm), which is equipped with an electric furnace of an upper layer of 36 cm silicon carbide (particle size 238 mm), heated to 350 ^° C., and a lower 15 cm layer (20 g ) made of silica gel (particle size 1.68 mm) has a surface area of 300m ² / g and a pore volume of 1 ccm / g. Water and dehydrated organic product are condensed and collected in the lower part of the column and separated. The organic product is dried and distilled. The distilled product is examined by infrared spectroscopy and vapor phase chromatography to find that it is 99+ mole percent styrene and less than 0.5 Mol% contains ethylbenzene. The overall yield based on alcohol is greater than 95%.

Example 2

A mixture of 50 parts of 4- {t-Buty!) - ix-niethy! Benzyl 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 up to a bed height of 203 to 22.9 cm filled with silica gel (particle size 1.68-238 mm), surface 34OmVg, 14 nm mean pore diameter and a sufficient amount of silicon carbide (particle size 336 mm) to fill the tube up to a total height of 41 cm. The reaction column is heated to 300 ⁰ C to 300 ⁰ C preheated water and the mixture are simultaneously supplied to the feed end of the column at rates of 90 ml / h and 45 ml / h The result is an intimate mixture of water vapor and alcohol in the vapor phase, the down over the pre-heated to 350 ⁰ C silicon carbide flows and this acts as a preheating zone for the steam Then, the mixture passes through the silica gel, the dehydration occurs after the passage through the silica gel water-organic product in the column are condensed and collected the dehydrated organic product is decanted, dried and distilled. The distilled product is examined by infrared spectroscopy and vapor phase chromatography to find 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-it-ButvHstvrols through

Heating in the presence of benzoyl peroxide produces a polymer that is soluble in toluene at 20 ° C.

Example 3

Some experiments in accordance with the procedure of Example 2 are carried out. With these Mixtures of 50 parts of 4- (t-butyl) - <x -methylbenzyl alcohol and 50 parts of toluene are used in experiments and mixed with different amounts of steam. The vapor 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 extends to different temperatures is preheated, and a lower bed of silica gel (the same as in example 2) from a height of 15 cm. At the bottom of the column

Table I.

10 water and the dehydrated organic product are 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 (C2 and C3) were carried out using different amounts of water in accordance with the same procedure. These results are also included in Table I.

Experiment no. Water / alcohol

Parts / part

Reaction temperature ')

⁰ C

Impurities ² ) Isopropenyl styrene

Mol%

4- (t-butyl) ethylbenzene Mol%

Polymer solubility ³ )

1 ~ 5.0 410 0 0.15 soluble 2 -1.4 406 0 0.15 soluble 3 -0.84 406 0 0.14 soluble 4th -0.56 395 0 0.13 soluble 5 -20.0 393 0 0.2 soluble 6th -20Ό 445 0 0.2 soluble 7th -20.0 505 <0.02 0.7 soluble 8th -0.50 400 0 0.1 soluble 9 -0.50 448 0 0.4 soluble 10 -0.50 506 <0.02 0.6 soluble C, *) -0 400 0.12 0.23 insoluble C ₂ *) -20.0 550 > 0, ll 1.4 insoluble C ₃ *) -0.50 550 > 0.18 1.5 insoluble

*) No example of the invention.

') The reaction temperature corresponds to the temperature of the silicon carbide used as a heat transfer medium.

² ) Specified impurity in mol%, based on moles of the p- (t-butyl) styrene produced; determined by gas phase chromatography and infrared spectroscopy.

³ ) Solubility of 10% p- (t-butyl) styrene polymer cream in toluene at 23 ° C.

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

ar-t-butyl-ÄA-dimethylbenzyl alcohol,
ar-dichloro-a-methylbenzyl alcohol,
ar-dibromo-a-methylbenzyl alcohol,
ar-di-t-butyl-Ä-methylbenzyl alcohol,
ar- (l -ethyl-1-methylpentyl) - <% - methyl-

benzyl alcohol,
ar-t-butyl-ar-methyl-a-methylbenzyl alcohol.

Some experiments using a silica gel catalyst of various particle size or mesh size and surface areas in the range of 300 to 900 m ² / g have also been carried out with good results

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 containing about 7 mole percent ar- (t-butyl) acetophenone, and 50 parts of toluene Glass column (outer diameter 2 ^ cm, length 41 cm) equipped with an electric furnace, the up to a height of 8.9 cm with silicon carbide (particle size 238 cm, 42 g) a total height of 34.2 cm with silica gel (the same as in example 2.50 g) and a total height of 41 cm was filled with silicon carbide (particle size 238 mm, 40 g), was used in the various attempts at temperatures from 200 to

50O ⁰ C heated. To at least 550 ⁰ C., superheated steam and the alcohol / toluene mixture the feed end of the column at rates of 100 ml / h were simultaneously (measured as condensed water) or / h fed 50 ml. An intimate mixture of water vapor and the alcohol mixture in the vapor phase was formed 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 II

10

10

To show conventional dehydration catalysts, some comparative tests (C4 - Cg) 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 70 m ² / g) was used instead 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- (t-butyl) - ar- (t-butyl) - ar- (t-butyl) - ar- (t-butyl) -o - methylstyrene

1 250 ° 2 350 ° 3 350 ° 4th 400 ° 5 450 ° 6th 500 ° C ₄ *) 250 ° C ₅ *) 300 ° C ₆ *) 350 ° C ₇ *) 400 ° C ₈ *) 450 °

Silica gel 92.1 Silica gel 95.3 Silica gel 95.9 Silica gel 97.2 Silica gel 95.3 Silica gel 94.2 anhydrous 97.3 Titanium dioxide anhydrous 97.2 Titanium dioxide anhydrous 94.1 Titanium dioxide anhydrous 91.9 Titanium dioxide anhydrous 83.5 Titanium dioxide

ethylbenzene acetophenone benzyl alcohol 0.5 4.4 3.0 0.3 4.5 - 0.3 3.9 - 0.2 2.6 - 0.2 4.5 - 0.5 5.3 - 0.4 2.3 - 0.6 2.2 - 1.9 4.0 - 5.4 2.7 - 12.3 3.3 _

*) No example according to the invention.

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

50 gen. 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

example

A solution of 50 parts of ar- (t-butyl) -Ä-methylbenzyl alcohol, which contains about 7 mol% of ar- (t-butyl) acetophenone in 50 parts of toluene, is mixed with steam superheated to 550 ° C. in a ratio of 2 parts Water mixed to a portion of the mixture. The steam-alcohol mixture is passed down through a glass column with an outer diameter of 23 cm and a length of 53 cm. The column contains a top layer of silicon carbide of 25.4 cm and a 25.4 cm lower layer of the same silica gel as in example 2. the temperature at the top of the column is 350 ⁰ C and distilled ° C. the water and the organic product wira on the ground 325 and its components are dried by vapor phase chromatography and infrared spectroscopy determined the results are in Table HI 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 mm), surface area 210m ² / g is used as the dehydration catalyst instead of silica gel. The organic product is distilled and dried. The results are also given in Table III

I. Tabel III catalyst 11th 27 36 948 Invention. m- (t-butyl) - ur- (t-bulyl) - 12th ar- (l-butyl) - ar- (t-butyl (acetophenone attempt styrene ethylbenzene toluene and ar- ar-ft-butylJ-ff-methyl- 1 No. (t-butyl) benzene benzyl alcohol, ppm I. Product composition, mol% 3.77 0.10 0.04 <25 ppm Silica gel p- (t-butyl) - 2.32 1.08 0.08 - 45 ppm I 1 slyrol I ^c "* ⁾ I *) None 96.09 Alumina 96.52 Example after the

Example 6

The dehydration process of the present invention is carried out in a continuous manner by continuously adding molten ar- (t-butyl) - «- methylbenzyl alcohol in an amount of 90.7 kg / hr and superheated water at 550 ° C 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 +%. The dehydrated product is identified as ar- (t-butyl) styrene by infrared spectroscopy.

Table IV Example 7

Some samples of ar-chloro - «- methylbenzyl alcohol, which contain small amounts of ar-chloro-acetophenone, are continuously dehydrated by mixing the liquid alcohol with different amounts of superheated steam (550 ° 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-boiling components are shown in Table IV. For comparison purposes, similar samples of ar-chloro-ec-methylbenzyl alcohol, which also contained small amounts of ar-chloro-acetophenone, were continuously dehydrated in the same manner, except that no water was added. The amount of the low-boiling components in these comparative experiments (C ₁₀ , C ₁₁ , C ₁₂ ) are also given in Table IV.

Sample No. water / alcohol reaction temperature

Low-boiling components of the reaction mixture, part ¹ )

ml / 100 ml ⁰ C 1 3 400 2 5 400 C ₁₀ *) 0 400 3 25th 350 C ,, *) 0 350 5 50 400 C ₁₂ *) 0 400

ar-chlorine- ar-chlorine- other styrene ethylbenzene 62.89 1.10 0.22 76.19 0.88 0.19 55.80 1.88 0.45 73.91 0.16 0.09 58.90 0.89 0.27 78.11 0.03 NB **) 63.64 1.61 0.45

Low boiling

Impurities /

ar-chlorostyrene

Parts / 100 parts

2.1

1.4

4.2

0.34

1.80

0.04

3.23

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

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

Example 8

Following the general procedure of Example 1, 4 different alkyl-a-methylbenzyl alcohols are blended with toluene and passed through a heated dehydration column Silica gel with a particle size of 1.68 mm and a surface area of 300 m ² / g.

The reaction products are separated and worked up in each case to the desired To obtain styrene homologs. The starting alcohols and the corresponding styrene homologues are below specified:

alcohol

t-amyl methylbenzyl alcohol

t-hexyl methylbenzyl alcohol

t-octyl methyl benzyl alcohol

t-dodecyl methylbenzyl alcohol

14th

Styrene homologs t-amyl styrene t-hexyl styrene t-methylethylpentyl-

styrene

t-dodecyl styrene

During the dehydration of this t-alkyl-Ä-methylbenzyl alcohol, in every case! the corresponding styrene homolog 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 of an α-methylbenzyl alcohol or an α-alkyl-substituted methylbenzyl alcohol of the general formula