Oxidative Chlorination of Ethylbenzene

1~4 M.S. SAZ,U~HOV et al.

10. G. M. GAL'PERN, V. A. IL'INA, P. M. SHUMSKAYA and V. N. ALEgSANDROV, Khlmlya i tekhnol, monomerov. Tr. Vses, n.-i. i proektn, in-t. monomerov 2, 129, 1970

11. A. M. IVANOV, L. N. KHAKALO and K. A. ~CHEItVINSKII, Neftel~hlmiya 8, 589, 1968

12. Ye. M. TOCHINA, L. M. POSTNIKOV and V. Ya. SHLYAPINTOKH, Izv. AN SSSR, Ser. khlm. 71, 1968

OXIDATIVE CHLORINATION OF ETHYLBENZENE AND ISOPROPYLBENZENE*

M. S. SAT, A~I~[OV, ~V~. ~~. GUSS]~I~OV, CH. A. CH~,A~IEV and D. K. ABD~LAYEV

Stungait Branch of the Institute of Petrochemical Processes Azerb. S.S.R. Academy of Sciences

(Received 16 July, 1974)

C~o~x~. derivatives of ethyl and isopropylbenzene are obtained by alkyiatiou of chlorobenzene in the presence of Friedel-Crafts [1, 2] catalysts by direct chlorination of ethylbenzene [3-5] and isopropylbenzene [6, 7]. A1Cls, FeCIa, ZnCI~, SnC14 and TiC14 are used as catalysts in chlorination of alkylbenzenes. However, secondary reactions [5, 7] are undesirable in the catalytic process of chlorination.

Investigations are being carried out in our laboratory in the field of oxi- dizing chlorination of alkyl-aromatic hydrocarbons [8]. There is no information in the literature about this problem.

This article is concerned with explaining some relations which govern the preparation of chlorine derivatives of ethyl- and isopropy!benzene by oxi- dative chlorination (with a mixture of hydrochloric acid and hydrogen pero- xide). .....

Experiments were carried out in a glass flask provided with a mechanical atirrer, drop funnel and a thermometer. Reaction temperature was maintained with an accuracy of 0.5 . Commercial hydrochloric acid, ethyl- and iso- pr0pylbenzene (pure) and a 30% aqueous solution of hydrogen peroxide were used: for the investigation. The flask was filled with these in given proportions. Hydrogen peroxide was added to the reaction mass from a drop funnel. ~ The react:ion mixture was analysed at equal time intervals by GLC using

an LKhM-7A device with a heat conductivity detector (detector current 90 mA).

* Neftekhlrnlya 15, No. 4, 601-605, 1975.

Oxidat ive chlorination of e~hylbenzene , 1~

Before chromatographic analysis the samples were washed o neutral reaction and dried over calcium chloride. Chromatographic curves were obtained using II~Z-600 brick modified with PEG-4000 at a carrier gas (nitrogen) velocity of 60 ml/min. The length of the column was 3 m, analytical temperature 150 .

Under these conditions the separation of products of the reaction mixture is ensured. The peaks were assigned by comparing the retention times of in- dividual compounds and those obtained. Results of chromatographic analysis and IR spectra of products synthesized show that o-, 10-ehloroethyl- and o-, ID-chloro-isopropylbenzenes are formed during the reaction.

%

/6

i I -I,

2oP ll / X / 1

~ I I I t J

0 ) # 6 8 10"c ,he I I I I

100 ZOO 300 400 500 r'pm

Fze. 1. Effect of the intensity of agitation of the reaction mass on the yield (1-6) and rate (7) of oxych]orination of ethy]benzene. Temperature 200, intensity of agitation,

rpm: 1--0; 2--100, 3--200; 4--300; 6--400; 6--600.

To find optimum conditions for oxychlorination, the.effects of the intensity of stirring the reaction mass, the concentration of hydrochloric acid, hydrogen peroxide feed rate, the molar ratio of reacting substances and temperature on the yield of chlorine derivatives of ethyl- and isopropylbenzene were examined.

RESULTS

In the initial stage of the experiment we determined the reaction range. Since initial a~omatic hydrocarbons (and chloroalkylaromatic compounds) do, not dissolve in hydrochloric acid it was assumed that reaction rate might be a~ected by difl~usion factors. In fact, results of experiments (Fig/ I )show that the intensity of sirring the reaction mixture has a marked effect on the field of monochloroethylbenzene and the rate of oxyehlorination.::: ThUs, without agitation (curve 1, Fig. 1) themaximum yield Of ehloroethylbenzene

'!156 M.S . SAT.A~OV ~ a/.

does not exceed 18%, while an increase in the intensity of agitation to 400 rev/min (curve 5) increases yield to 91/o. A further increase of agitation intensity to 600 rev/min has no effect on the yield of chlo~oethylbenzene. To obtain comparable results by a di~erential method, initial reaction rates were calculated at dii~erent intensities of agitation.

A marked increase in reaction rate in the interval of 200-400 rev/min (Fig. 1, curve 7), apparently, points to a transition of the reaction from the diffusion (

Oxidative chlorination of ethylbenzene 157,

Results of Fig. 2 indicate that the yield of ehloroethylbenzene and the rate of its formation depend on the concentration of hydrochloric acid and the reaction does not take place in practice if acid concentration is lower than 12~o. An increase in He1 concentration to 36% increases the yield of chloro- ethylbenzene to 91% in 2 hr.

Oxidative chlorination of aromatic hydrocarbons depends both on reaction (1) and reaction (2). I f the rate of reaction (2) is equal to, or considerably higher than, the rate of reaction (1) the separation of free chlorine may be excluded. I t was established that without aromatic compounds reaction (1) takes place at a high rate and it may be adjusted by the rate of hydrogen peroxide supply. Consequently, it was essential to select conditions under which the chlorine separated in the first stage fully reacted with aromatic hydrocarbons. Results in Fig. 3 indicate that a feed rate of hydrogen peroxide of 10 g/hr is optimum; at this rate a 98-99~/o yield of chloroethylbenzene is ensured in terms of the hydrogen peroxide taken. The Figure shows that with the simultaneous supply of all reacting substances the rate of oxidative chlorination is higher than with the gradual feed of Hz0~, but the yield of chlorine derivatives is only 790/0, i.e. part of chlorine is not used up in the reaction.

TABLE 1. EFFECT OF ~:J~JS AMOUNT OF HYDROGEN CHLORIDE ON T~lJ~ ~2"J[ELD OF CHLORO-

"~.~t"Y'L- AND CHLOROISOPROP~irLBENZ]ENE8

Temperature 20C; molar ratio of alkylbenzene : H,O~----1 : 1

HC1, mole

1 2 4 6 8

10

Yield, % C,HsC,H,C1

overall I

28 57 85 91 91 91

o-I 17 11 35 22 52 33 55 36

i 55 36 56 35

C~IIC,HsC1, p-

0 2 4 7 7.5 8

CsH~C6H,C1 veraU I " I P"

23 11 112 51 25 26 7O 34.5 35.5 80 39.5 40.5 81 40 i 41 82 40"5 I 41.5

CsH,CeH,CI~

2.5 5 8 11 11

The effect of the amount of hydrochloric acid in the initial mixture on the yield of chloroalkylbenzenes is shown in Table 1. Investigations were carried out at an intensity of agitation of the reaction mixture of 400-450 rev/min and a rate of hydrogen peroxide feed of 10 g/hr. An increase in the molar concentration of hydrochloric acid from 1 to 6 moles pet mole hydrogen peroxide increases the yields of monochloroethylbenzene and monochloro- is0propylbenzene from 28 to 91% and from 23 to 80%, respectively.

The relatively low yield of monochloro-isopropylbenzene, particularly o-isomers is probably due to the sterie effect of the isopropyl radical (Tables 1 and 2). A further increase in the content of hydrochloric acid increases tho

158 1~. S. SAT.Alg'Frov et a~=

formation of dicMoroderivatives of aromatic compounds, the yields of which vary between 8 and 11 ~.

A study of the effect of temperature on the yields of chloroaromatic hydro- carbons in the temperature range of 0-40 at a rate of hydrogen peroxide feed of 10 g/hr (Fig. 4a, b) indicates that an increase in temperature accelerates oxychlorination of ethyl- and isopropylbenzenes. The time to achieve a maxi- mum yield of the intermediate product at 40 decreases from 9 to 3 hr, this yield, however, is lower than at 0 . This dependence of the yield of ehloroethyl- benzene on temperature is due to the. acceleration of subsequent chlorination of the chloroethylbenzene formed to dichloroethylbenzenes. In fact, it follows from curves 2'-5' (Fig. 4a) that with an increase of temperature from 10 to 40 , diehloroethylbenzene yield varies between 4 and 18~o and at 0 the latter is not formed at all. Consequently, to achieve selective oxychlorination, the process should be carried out at low temperature (20 and lower) or at high temperatures with a duration of up to 3 hr.

a/a / 100 a 3 b

1 3 5 7 8 I 8 5 7 r ,h r

FIG. 4. Dependence of the yields of chloroaromatic hydrocarbons on reaction t ime: a - - chloroethyl (1-5) and dichloroethylbenzene (2'-5"); b -- chloroisopropyl (1-4) and dichloroisopropyl benzene (1'-4'). Molar ratio of C6HsAI HC1 : H=O----1 : 6 : 1; tempera

ture, C: 1--0; 2, 2'--10; 3, 3'--20; 4, 4'--30; 5, 5'--40.

Similar results were obtained for oxychlorination of isopropylbenzene (Fig. 4b). In this case with an increase of temperature the yield of monochloro- isopropylbenzene decreases and the content of dichloroisopropylbenzene in- creases.

Results in Fig. 4 indicate that the formation of dichloroderivatives of ethyl- and isopropylbenzenes begins after a 45~ conversion of initial alkyl- aromatic compounds. Therefore, in order to increase process selectivity, a study was made of the effect of molar quantitites of ethyl- and isopropyl- benzenes in the reaction mixture (Table 2).

Oxidative chlorination of ethylbenzene 159

I t was found that with an equimolecular rat io of aromat ic hydrocarbons and hydrogen peroxide up to 7-8~/o dichloroderivatives are formed.

T~BLE 2. EFFECT OF ~ '~ MO~ PROPORTION OF ETJ~t~Jb-AND ISOPROPYI,BEN~ENES ON '~ Y IELD OF MONO- AND DICH~LOROA_ I .~Y I ,BENZENES

Temperature 20C hydroperoxide feed rate 10 g/hr; molar ratio of HCI:HIOs =6:1

Alkyl- benzene,

mole

1 2 4 6 8

10

CIHsC,H~C1

overall o- p-

91 55 36 93 57 37 95 58 37 96 58 38 96 58 38 97 59 38

I C,H6C,HaC1. CaHTCeH,C1

overall o -

80 39.5 94 46-5 95 47 96 47.5 97 48 97 48

p-

40"5 47"5 48 48"5 49 49

CsHTC,HaCII

On increasing the molar rat io of alkylbenezene: hydrogen peroxide to 10 : 1, the contents of dichloro-derivatives decreases to 1.0~/o and the yield of monochloro-alkylbenzenes increases to 97.0%.

SUMMARY

l . A s tudy was made of oxychlor inat ion of ethyl- and isopropylbenzene wi th a mixture of hydrogen peroxide and hydrochloric acid. I t was shown that wi th vigorous st irr ing (over 400 rev/min) the reaction takes place in tho k inet ic range.

2. On using 36~/o hydrochloric acid and a molar rat io of Ar : HCI : H20a of 1 :1 :1 , yields of chlorethyl- and chlorisopropylbenzenes are 28 and 23 and wi th a rat io of 1 : 6 : 1 they increase to 91 and 80~/o, respectively. An increase in the concentrat ion of the aromat ic compound to 10 mole results in the format ion of ortho- and para-isomers.

REFERENCES

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and P. A. PETROSYAN, Azerb. khim. zh. No. 4, 9, 1962 5. Yu. S. KROPANEV, V. G. PLYUSNIN, N. I. PLOTKINA and L. P. UL'YANOVA,

Neftckl~imlya 9, 591, 1969 6. Yu. G. MAMEDALIYEV, Izbrannyye proizvcdcniya (Selected Works), Izd. AN Azerb.

SSR 1, 1964 7. Yu. S. KROPANEV, V. G. PLYUSNIN and P. I. PLOTKINA, Ncftebhimiya 7, 398,

1967 8. Auth. Cert. U.S.S.R. 386891, 18. 10. 1972. Otkr. isobr., prom. obr. i toy. znaki, No. 27,

59, 1973