Table 2. Effect of different PTC on the rate and selectivitya
Table 4. Effect of temperature on the rate and selectivity of
oxidative chlorination of 4-methylphenol under
phase-transfer conditionsa
PTC
% conversion % selectivity
tetraheptylammonium chloride
tetrahexylammonium chloride
tetrabutylammonium chloride
100
98
97
99.8
99.7
99.8
temperature (°C)
% overall conversion
% selectivity
35
57
100
100
100
99.8
89
4
5
5
5
a
Reaction conditions: reactant concentration, 2.3 mol/L of organic phase;
hydrochloric acid, 3.85 mol/L of aqueous phase; hydrogen peroxide, 1.926 mol/L
of aqueous phase; PTC, 1.9 mol % of the substrate; organic phase, 25 mL;
aqueous phase, 30 mL; temperature, 45 °C; reaction time including addition
time, 2 h.
a
Reaction conditions: reactant concentration, 2.3 mol/L of organic phase;
hydrochloric acid, 3.85 mol/L of aqueous phase; hydrogen peroxide, 1.926 mol/L
of aqueous phase; PTC, 1.9 mol % of the substrate; organic phase, 25 mL;
aqueous phase, 30 mL; reaction time including addition time, 2 h.
Table 3. Oxidative chlorination of 4-methylphenol in
different organic solventsa
Table 5. Effect of mole ratio of reactant to hydrogen
peroxide in the oxidative chlorination of 4-methylphenol
a
solvent
% overall conversion
% selectivity
%
selectivity to % selectivity to
ethylenedichloride
carbontetrachloride
chloroform
100
98
100
96
99.8
99.5
100
99
% overall
monochloro
dichloro
reactant: H O
2
2n
conversion
compound
compound
1
,1,1-trichloroethane
1
1
1
1
:0.5
:0.9
:1
50
90
100
100
100
100
99.8
54
0
0
0.1
45
a
Reaction conditions: reactant concentration, 2.3 mol/L of organic phase;
hydrochloric acid, 3.85 mol/L of aqueous phase; hydrogen peroxide, 1.926 mol/L
of aqueous phase; PTC, 1.9 mol % of the substrate; organic phase, 25 mL;
aqueous phase, 30 mL; temperature, 45 °C; reaction time including addition
time, 2 h.
:1.5
a
Reaction conditions: Reactant concentration, 2.3 mol/L of organic phase;
hydrochloric acid, 3.85 mol/L of aqueous phase; tetraheptylammonium chloride,
1
.9 mol % of the substrate; organic phese, 25 mL; aquous phase, 30 mL;
temperature, 45 °C; reaction time including addition time, 2 h.
Conditions. Column used, 30-m Crossbond 5% di-
phenyl-95% dimethylpolysiloxane; ID, 0.53 mm; supplier,
Restek Corp; carrier gas, helium; flow rate, 15 mL/min;
injector temperature, 300 °C; detector temperature, 300 °C;
oven temperature, 120 °C, 2 min, 8 °C/min, 200 °C, 5 min.
Table 6. Optimum conditions and isolated yield with 100%
material balance for the oxidative chlorination of
4
-methylphenola
overall conversion of 4-methylphenol
selectivity with respect to monochloro compound
conversion to dichloro compound
tarry material
100%
99.8%
0.12%
0.08%
96%
Results and Discussion
Definitions. ConWersion. The conversion is defined as
the ratio of the moles of the reactant reacted to the moles of
the reactant taken.
SelectiVity. The selectivity to a particular product is
defined as the ratio of the moles of the reactant reacted for
the formation of that particular product to the moles of
reactant reacted.
isolated yield
a
Reaction conditions: reactant concentration, 2.3 mol/L of organic phase;
hydrochloric acid, 3.85 mol/L of aqueous phase; hydrogen peroxide, 1.926 mol/L
of aqueous phase; PTC, 1.9 mol % of the substrate; organic phase, 25 mL;
aqueous phase, 30 mL; temperature, 45 °C; reaction time including addition
time, 2 h.
Process Parameter Studies. Different important process
parameters were studied to develop the most suitable reaction
conditions for obtaining the maximum selectivity to the
desired product under the reaction conditions. All of the
reactions for process parameter studies were performed in
semi-batch manner where hydrogen peroxide was added
dropwise to the reaction mixture.
tetrachloride, chloroform, and 1,1,1,-trichloroethane. It was
observed that the rate and selectivity was maximum in
chloroform, but the same selectivity was achieved in almost
each of these solvents (Table 3).
The oxidative chlorination of 4-methyphenol was studied
2 2
by using HCl-H O over a wide range of temperature. At
With an increase in addition time, the overall conversion
of 4-methylphenol increased as usual but the selectivity also
increased (Table 1). This is due to the increase in rate of
formation of dichloro compund at a faster hydrogen peroxide
addition. It was observed that a 1.5 h addition time was
preferred under these reaction conditions to obtain maximum
35 °C, only 57% conversion was obtained in 2 h (Table 4).
When the temperature was increased to 45 °C the conversion
of 4-methylphenol increased to 100%. However, with a
further increase in temperature from 45 to 55 °C, the
selectivity decreased from 100 to 89%. This is due to the
faster rate of side reactions leading to the dichloro and isomer
formations at the higher temperature.
2 2
selectivity and H O utilization.
Different PTC like, tetraheptylammonium chloride, tetra-
hexylammonium chloride, and tetrabutylammonium chloride
were used, and it was observed that any one of these PTC
could be used as the conversion and selectivity obtained was
almost the same, (Table 2).
From stoichiometry, to form one mole of monochloro
compound, one mole of hydrogen peroxide and one mole of
hydrochloric acid are needed for one mole of reactant.
Different molar ratios, 1:1.5, 1:1.75, and 1:2 of HCl to
substrate have been used, and in 2 h, the conversions were
65, 84, and 100, respectively. In all of the reactions carried
out, hydrochloric acid was used at 2 mol/mol of reactant to
The rate of oxidative chlorination of 4-methylphenol was
examined in different solvents, for example, EDC, carbon-
510
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Vol. 4, No. 6, 2000 / Organic Process Research & Development