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The Dichlorocyclopropanation of Styrene and P-Chloromethyl Styrene Using Water Soluble Multi-Site Phase Transfer Catalyst A Kinetic Study

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ISSN 2319-7625 (Online) (An International Research Journal), www.chemistry-journal.org

The Dichlorocyclopropanation of Styrene and

P-Chloromethyl Styrene Using Water Soluble

Multi-Site Phase Transfer Catalyst –

A Kinetic Study

Kannan Shanmugan and Kamalakannan Sasikala

Department of Chemistry,

Government Arts College, Chidambaram, Tamil Nadu, INDIA.

(Received on: August 6, 2015)

ABSTRACT

The present study focuses the attention towards the utility of multi-site phase transfer catalyst (MPTC), is demonstrated by studying hydroxide-ion initiated reaction like dichlorocarbene addition to olefins. The formation of the product was monitored by GLC. Dichlorocyclopropanation of styrene and p-chloro methyl styrene catalyzed by multi-site phase transfer catalyst carried out in biphase medium under pseudo-first-order conditions by keeping aqueous sodium hydroxide and chloroform in excess. The effect of various experimental parameters on the rate of the reaction has been studied. Also thermodynamic parameters such as ∆S#, G# and H# were evaluated; based on the experimental results, a suitable mechanism is proposed. It also deals in greater detail on the kinetic aspects of chosen reactions. An attempt has been made to compare the ability of MPTC-I with MPTC-II and single-site PTC for dichlorocarbene addition to olefins like styrene and p-chloro methyl styrene.

Keywords: Multi-site phase transfer catalysts, Dichlorocyclopropanation, Styrene,

p-chloro methyl styrene, kinetics.

INTRODUCTION

The addition of dichlorocarbene to olefins1,2 has provided an exceptionally useful

synthesis of gem -dihalocyclo alkanes. When acyclic olefins are employed, the dihalides are relatively stable but certain cyclic olefins have been found to undergo rearrangement to ring expanded products3. Literature reports of the generation and reaction of dichlorocarbene stress

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carried out in bi - phase systems of concentrated sodium hydroxide in the presence of PTCs4.

Since the addition of a dichlorocarbene to an olefin assuredly must be a highly exothermic process5,7, the demonstration of the electrophilic nature of the carbenes8,9 has provided amble

evidence for the polar contribution to the transition state of the carbene - olefin reaction10.

Similar studies employing PTCs for the generation of dichlorocarbene were reported by several authors11,12 . The kinetic experiments (followed by GC) of the dichlorocarbene addition

to styrene and p-chloro methyl styrene were carried out under pseudo - first order conditions, taking chloroform and 15% aqueous sodium hydroxide in excess at 450C (Scheme 1,2.

dichlorocarbene addition to styrene and p-chloro methyl styrene under PTC conditions).

Dichlorocarbene addition to styrene and p-chloromethyl styrene under PTC conditions

Effect of stirring speed

The effect of varying the stirring speed on the rate of Dichlorocarbene addition to reaction using MPTC - I was studied in the range of 100 - 700 rpm. The rate of the reaction increases sharply as the stirring speed is increased up to 500 rpm in the case of styrene and p-chloro methyl styrene (Table.1, Fig.1). The effect of varying stirring speed is well documented for interfacial mechanisms, which are transfer rate - limited9,13,14 (the rate constant

increases with stirring ) below a given stirring speed (600 – 700 rpm) and intrinsic reaction rate limited (the kobs is nearly a constant) above this stirring speed. Similar behavior is

displayed by reactions with a real “ phase transfer’’(Stark’s Extraction mechanism) but with a much smaller limit of stirring speed between physical and chemical control (100 – 300 rpm).In the present study, the rate constants of the reaction increases as stirring speed increases and levels off to a constant value above the optimum stirring speed (500 rpm). Halpern et al.15

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Kannan Shanmugan, et al., J. Chem. & Cheml. Sci. Vol.5 (8), 448-457 (2015) 450

increase in the interfacial area per unit volume of dispersion with the corresponding increase in the speed. Thus increasing the stirring speed changes the particle size of the dispersed phase. Above certain stirring speed (500 rpm), the particle size does not change. The constancy of the rate constants is observed not because the process is necessarily reaction rate limited but because the mass transfer rate has reached constant value. Therefore Fig. 1 (Table.1) are indicative of an interfacial mechanism and not of a real “Phase Transfer’’.

Effect of Substrate Amount

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Table.1.Effect of MPTC-1 on the rates of dichlorocarbene addition to styrene and p-chloromethyl styrene reactions

Type of variation variable parameters Rates of the reaction (kobs x 104, S-1) ---

Styrene p-chloromethyl styrene

Stirring speed (rpm) 100 0.43 2.22

200 0.54 3.17

300 0.73 3.74 400 1.68 4.80 500 1.84 4.81 600 1.85 4.81 700 1.85 4.83 800 1.87 4.85 Substrate 5.31 2.54 7.47 Amount 10.62 1.89 3.53

(mmols) 15.93 1.56 3.42

21.24 1.24 2.60 26.55 0.88 1.40 31.86 0.65 1.30 Catalyst 0.10 0.36 2.98 Amount 0.15 0.63 2.41

(mmols) 0.20 1.22 4.91

0.25 1.46 5.90 0.30 2.59 7.23

[NaOH] (M) 3.41 0.53 2.73

4.41 0.87 4.42

5.49 1.29 4.93

6.65 1.59 5.37

7.89 1.88 6.61

Temperature 313 0.44 3.57

(K) 318 0.72 4.31

323 0.89 4.88

228 1.35 6.56

333 1.67 7.24

Effect Catalyst Amount

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Kannan Shanmugan, et al., J. Chem. & Cheml. Sci. Vol.5 (8), 448-457 (2015) 452

experiments were carried out and these showed absolutely no conversion even after three hours of the reaction. The linear dependence of reaction shows that the reaction is believed to proceed through the extraction mechanism. A bilograthmic plot on the observed rate constant against the concentration of the catalyst gives a straight line over a wide range of catalyst concentration 0.10 - 0.30 mol% for styrene and p-chloro methyl styrene (Table.1, Fig. 3). The slope of 4.52 for dichlorocarbene addition to styrene was found to be identical with the slope of the same reaction carried out in the presence of benzyl triethylammonium chloride (BTEAC) by Balakrishnan et al.16. This result suggests that the chemical reaction is not the slope rate -

determining step. A slope of 1.46 for p-chloro methyl styrene were obtained graphically (Fig. 3).The fore given observation enables one to predict that the carbanions formed cannot leave the phase boundary to go into the organic phase since their counter ions (Na+) are

strongly solvated in the aqueous phase and poorly in the organic phase. In the “absorbed’’ state, the carbanions are very unreactive being able to react only with strong electrophiles. The “multi -site’’ quaternary ammonium cations were able to the organic phase soluble ion - pairs with carbanions thus enabling them to pass into the organic phase for further transformation. The remarkable increase in yield of the dichlorocarbene adduct reflects the ability of the quaternary salt to cause : CCl2 to be generated in or transferred to be the organic phase where

its reaction rate with the substrate is much greater than with water as reported by Stark’s in the study of dichlorocarbene addition to cyclohexene using tridecyl methyl ammonium chloride17.

Effect of Sodium hydroxide Concentration

The rate of dichlorocarbene addition reaction, strongly depends18 on the concentration

of NaOH. The reaction rates were measured in the range 3.41 - 7.89 mol dm-3 for styrene and

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Influence of temperature variation

The effect of varying temperature on the rate of dichlorocarbene addition reaction to styrene and p-chloro methyl styrene were studied in the temperature range 40 – 600C. The

kinetic profile of the reaction is obtained by plotting log (a-x) versus time. The rate constants increase with increase in temperature for styrene and p–chloro methyl styrene (Table.1, Fig. 5). The thermodynamic Parameters ∆H#, S#,and G# are evaluated and presented. The

three energy of activation of intra – particle diffusion of anion exchange resins in aqueous solutions is of the order 5 10 Kcal mol-1.The activation energy for the dehydrobromination of

(2-bromoethyl) benzene19 in the presence of tetra ammonium bromide was reported to be 12.41

Kcal mol-1 and for this an extraction mechanism was proposed20. The observed energy of

activation (Ea) for dichlorocarbene addition to styrene and p-chloro methyl styrene are found to be 9.7 Kcal mol-1 and 10.6 Kcal mol-1. Hence we conclude that since the intra - particle

diffusion is minimized at 500 rpm, the intrinsic reactivity is the rate – limiting step.

Table .2: Thermodynamic Parameters

Substrate Ea Kcalmol

-1 ∆H

#

Kcalmol-1 ∆S

# CalK-1

mol-1 ∆G

# Kcalmol-1

Styrene 9.7 9.1 -178.3 56.3

p-chloro methyl styrene 10.6 10.0 -172.0 53.9

Comparison of reaction rate constants with different catalysts

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Kannan Shanmugan, et al., J. Chem. & Cheml. Sci. Vol.5 (8), 448-457 (2015) 454

taking 20 ml chloroform, 0.1 mol% catalyst (MPTC-I) and 25% w/w NaOH. The reactions were run at 450C with a stirring speed of 500 rpm. The observed rate constants (k

obs x 104, S-1)

for styrene and p-chloro methyl styrene are found to be 3.08 and 5.35 respectively (Table .3). These values are in an approximate ratio 7:4 (P-chloro methyl styrene: styrene). The reaction rate of p-chloro methyl styrene is 1.75 times faster than styrene and this can be attributed to the comparative electron - rich nature of olefinic double bond of p-chloro methyl styrene. Also the transition state of p-chloro methyl styrene is far less hindered than styrene which makes p- chloro methyl styrene more reactive than styrene. The reaction, dichlorocarbene addition to olefins such as styrene and p-chloro methyl styrene have been chosen to investigate the comparative reactivities of three different catalysts, viz., MPTC-I, MPTC-II and soluble “single-site” PTC (triethyl benzyl ammonium chloride-TEBAB). The reaction conditions employed are 15% w/w aqueous sodium hydroxide, 20ml chloroform, 500rpm stirring and 2.0ml/2.0g substrate. All the reactions were carried out at the same temperature, 45oC. The

reaction rates and the amount of catalysts used are listed below:

Table :3. Comparison of reaction rate constants with different catalysts

Entry Catalyst Amount (mol %) kobs /10-4,S-1

    Styrene p-chloro methyl styrene

A None None Nil* Nil*

B MPTC-I 0.1 3.08 5.35

C MPTC-II 0.1 2.01 3.16

D SPTC 0.1 0.45 2.00

The above results reflect a comparative trend among the different catalysts used. Based on the observed rate constants, it is evident that the MPTC-I is 60% and 75% more active than the MPTC-II and “single-site’’TEBAB respectively.

“Multi - site’’ Phase Transfer Catalyst - I’s activity in hydroxide - ion initiated reactions

The results shown in Table.4 establish the synthetic utility of the new MPTC-I under PTC/ OH- conditions. Control experiments of dichlorocarbene addition to olefins in the

absence of the catalyst resulted in < 1% conversion in three hours. As is evident from Table .4, the new MPTC catalyst - I is found to perform extremely well for hydroxide - ion initiated reaction systems resulting in excellent yields of the products. All the dichlorocarbene addition reactions were conducted at identical reaction conditions taking 20ml chloroform, 0.1 mol% catalyst (MPTC-I) and 25% W/W NaOH. The reactions were run at 450C with a stirring speed

of 500 rpm. The reaction, viz., dichlorocarbene addition to olefins such as styrene and p-chloro methyl styrene, in presence of MPTC – I resulted in 100% conversion within one hour.

MECHANISM

A chloroform when treated with concentrated aqueous sodium hydroxide and a quaternary ammonium salt, Q+X- (as a PTC) generates trihalomethyl anion which further splits

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PTC conditions) towards alkenes are independent of the structure of catalysts. This indicates that free : CX2 is involved in all cases in spite of the fact that there is a strong catalyst influence

on reaction path starting from Cx3- into :CX2 . Scheme 1 and 2 shows the mechanism for the

dichlorocarbene addition to styrene and p-chloro methyl styrene under PTC conditions25.

According to Stark’s Extraction mechanism, it was thought that the hydroxide ion may be extracted from an aqueous reservoir into an organic phase with the help of quaternary Onium cations. Makosza and Biolecka26 proposed an alternative mechanism for dichlorocarbene

addition reactions in which deprotonation of the organic substrate by the hydroxide - ion occurs at the interface. According to this mechanism, the role of catalyst is to remove the resulting organic anion from the interface into the bulk organic phase for subsequent reaction. Several studies have provided support for various aspects of Makosza’s mechanism. It has been established by Makosza and Fedorynski that the slowest reaction is the addition of: CCl2 to

olefins, considering the other steps as fast equilibrium processes. In our study, a fractional order with respect to the catalyst concentration suggests that step (2) is not the sole rate - determining one and that the chemical reaction in the organic phase is also rate - determining. The effect of other experimental parameter such as stirring speed, sodium hydroxide concentration and temperature over the observed rate of the reaction support the interfacial mechanism proposed by Makosza for PTC/OH- systems. The generation and reaction of

carbene with styrene and p-chloro methyl styrene may represent as follows;

3CHCl3 + 3NaOH 3CCl3-Na+ + H2O

(org) (aq) (interface)

MPTC (org) fast (2)

3:CCl2 + MPTC

(org) (org)

3 C CH2

C

Cl Cl

H

(Scheme-3)

Ph CH(OH)-C[CH2N+Et3 CCl3-]3 + 3NaBr

(org) (aq)

fast(3)

(A) fast(1)

3 C

H CH2

Slow(4)

H2C

Cl

3

(A)

Slow(4)

(Scheme - 4)

CH

H2C CH2

Cl 3

Cl Cl

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Kannan Shanmugan, et al., J. Chem. & Cheml. Sci. Vol.5 (8), 448-457 (2015) 456

Table .4: Hydroxide – ion initiated reactions under the PTC conditions using the new MPTC - I

S.

No Substrate with experimental conditions Products (S) % Conv a with

Reaction time Spectral data

b Reference

1 Styrene (1.09min.)

1. Subs. amount: 2.0 ml

2. Cat. amount: 7.04mg (0.1 mol%) 3.Solvent: CHCl3, 20 ml

4. [NaOH]: 25% w/w 25ml (8.33M) 5 Temp. 50oC

Product –I (1.44min.) Cl Cl 100.00; One hour 1H-NMR CDCl3/TMS)

δ=7.31 (s,5H, aromatic), 3.13-2.78 (t,lH), 2.14 – 1.82 (dd, 2H),

21

2 p-chloro methyl styrene (0.95 min.)

CH2

Cl

1. Subs. amount: 2.0 ml

2. Cat. amount: 7.04mg (0.1 mol%) 3.Solvent: CHCl3, 20 ml

4. [NaOH]: 25% w/w 25 ml (8.33M) 5 Temp. 50oC

Product – I (1.33 min.) H Cl Cl CH2 Cl 100.00; One hour 1H-NMR CDCl3/TMS)

δ=7.06 (s,5H,aromatic), 2.97 – 2.64 (t,1H), 2.33 (s. 3H), 1.92-1.76 (dd,2H)

22

a: Conversion by Gas chromatography, b: for known compounds only selected spectral data given

ACKNOWLEDGEMENTS

The author would like to thank the Principal and Head of the Department of Chemistry of Government Arts College, C.Mutlur, Chidambaram-608 102, Tamil Nadu for their grant of permission to do this research work.

REFERENCES

1. W. H . Urry, J.R. Eizner, J. Org. Chem., 73, 2977 (1951).

2. J . D. Roberts, V . C. Chambers, J . Org. Chem., 73, 5034 (1951).

3. C . W. Jefford, W . G. Graham, U. Burger, Tetrahedron Let., 4717 (1975).

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5. Y. Wang, Z. Zhang, Z. Zhen, J. Meng, P. Hodge, Chines J. Polymer Sci., V16, 356 – 361

(1998).

6. G. L. Closs, R. A. Moss, J. J. Coyle, J. Am. Chem. Soc., 84, 4985 (1962).

7. E. J. Corey, F. Xu, M. C. Noe, J. Am. Chem. Soc., 119, 12414 (1997).

8. E. V. Dehmlow, Tetrahedron Lett., 91 (1976).

9. M. R.Abonivitz, Y. Sasson, M. Halpern, J. Org. Chem., 48, 1022 (1983).

10. A. Brandstrom, S. Junggren, Acta. Chem. Scan., 23,2204 (1969).

11. E. J. Fendler, J. H. Fendler, Adv. Phys. Org. Chem., 8, 271 (1970).

12. A. Yu. Egorova, V. A. Sedavkina, Z. Yu. Timofeyeva, Molecules, 5, 1082 – 1084 (2000).

13. E. V. Dehmlow, S. S. Dehmlow, In “ Phase Transfer Catalysis’’ VerlagChemie, Wein Heim (1993).

14. W. P. Reeves, R. G. Hilbirch, Tetrahedron, 32, 2235 (1976).

15. M. Halpern, Y. Sasson, I. Willner, M. Rabinovitz, Tetrahedron Lett., 1719 (1981).

16. T. Balakrishnan, T. K. Shabeer, K. Nellie, Proc. Indian, Acid. Sci., (Chem. Sci., ) 103,

785 (1991).

17. C. M. Starks, J. Am. Chem. Soc., 93, 195 (1971).

18. F. Helfferich, In “Ion Exchange Resins’’ , McGraw Hill, New York (1962). 19. M. Halpern, Y. Sasson, M. Rabinovitz, J. Org. Chem., 49 2011 (1984).

20. M. Halpern, Y. Sasson, M. Rabinovitz, Tetrahedron, 38, 3138 (1982).

21. K.Shanmugan,E.Kannadasan, J. of Chem. and Chem. Sci.,4,176-191(2014).

22. K. Shanmugan, E. Kannadasan, Int. J. Curr. Microbiol. App. Sci.3 (9),211-223 (2014).

23. M. Fedorynski, W. Ziolkowski, A. Jonczyk, J. Org Chem., 58, 6120 (1993).

24. B. Lygo, P. G. Wainwright, Tetrahedron Lett., 38, 8595 – 8598 (1997).

25. E. V. Dehmlow , V. Fastabend, J. Chem. Soc., Chem. Commun., 16, 1241 (1993).

Figure

Table .2: Thermodynamic Parameters
Table :3. Comparison of reaction rate constants with different catalysts
Table .4: Hydroxide – ion initiated reactions under the PTC conditions using the new MPTC - I

References

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