Vicinal glycol ester preparation process

Claim 2

IN THE PROCESS FOR THE CONTINUOUS PREPARATION OF C1-C5 HYDROCARBY ALIPHATIC ACID ESTERS OF C2-C3 VICINAL GLYCOLS BY THE CATALYTIC LIQUID PHASE REACTION OF (A) AN OLEFINE CORRESPONDING IN STRUCTURE TO THE GYCOL MOIETY OF SAID ESTER AND SELECTED FROM THE GROUP CONSISTING OF ETHYLENE AND PROPYLENE, (B) MOLECULAR OXYGEN AND (C) A MONOBASIC ALIPHATIC HYDROCARBYL CARBOXYLIC ACID OF 1-5 CARBON ATOMS CORRESPONDING IN STRUCTURE TO THE ACYL MOIETY OF SAID ESTER, THE CATALYST FOR SAID REACTION BEING A TELLURIUM OR SELENIUM CATION IN COMBINATION WITH A HALIDE ANION, THE COMBINATION BEING SELECTED FROM THE GROUP CONSITING OF TELLURIUM CATION PLUS BROMIDE ANION, SELENIUM CATION PLUS BROMIDE ANION AND SELENIUM CATION PLUS CHLORIDE ANION, SAID REACTION BEING CARRIED OUT WITHIN AN OXIDATION ZONE CONTAINING A LEQUID PHASE REACTION MEDIUM COMPRISING REACTION, CATALYST AND REACTION PRODUCTS INCLUDING THE CARBOXYLIC ACID ESTER AND HALOGENATED BYPRODUCTS, WHEREIN REACTANTS ARE CONTINOUSLY INTRODUCED INTO THE OXIDATION ZONE AND LEAST A PORTION OF THE LIQUID PHASE REACTION MEDIUM IS CONTINUOUSLY WITHDRAWN, THE WITHDRAWN PORTION OF THE REACTION MEDIUM BEING PROCESSED TO RECOVER CARBOXYLIC ACID ESTER PRODUCT, UNCONVERTED AND HALOGENATED BY-PRODUCTS AND WHEREIN THE RECOVERED UNCONVERTED REACTANTS ARE RECYCLED TO THE OXIDATION ZONE, THE IMPROVEMENT WHICH COMPRISES MINIMIZING SELECTIVITY LOSSES WHILE MAXIMIZING RATE OF FORMATION OF CARBOXYLIC ACID ESTER PRODUCT BY RECYCLING AT LEAST A PREDOMINANT PORTION OF THE HALOGENATED BYPRODUCTS TO THE OXIDATION ZONE TO PROVIDE A SUBSTANTIAL PORTION OF THE HALOGEN COMPONENT OF THE CATALYST SYSTEM WHILE CONDUCTING THE REACTION AT A TEMPERATURE EXCEEDING 150*C. BUT NOT IN EXCESS OF ABOUT 250*C. IN THE PRESENCE OF AT LEAST 0.05 EQUIVALENT OF A BASICITY CONTROL CATION PER GRAM-ATOM OF HALOGEN ANION IN THE LIQUID PHASE REACTION MEDUM, SAID BASICITY CONTROL CATION HAVING, WHEN IN THE FORM OF SALT WITH THE HALIDE CORRESPONDING TO THAT OF THE CATALYST SYSTEM, AN ACTIVITY COEFFICIENT OF AT LEAST 0.40 AND SAID BASICITY CONTROL CATION NOT HAVING A PHREDUCING EFFECT WHEN IN THE FORM OF SALT WITH THE CARBOXYLIC ACID REACTANT, THE BASICITY CONTROL CATION BEING SELECTED FROM AT LEAST ONE MEMBER OF THE GROUP CONSISTING OF THE ALKALINE EARTH METALS, THE LANTHANIDES, SCANDIUM,YTTRIUM, IRON, COBALT, NICKEL, ZINC, BISMUTH, CHROMIUM, MANGANESE, MOLBDENUM, COPPER, ARSENIC, ANTIMONY, ALKYL, ALKYL AMINES, ALKYL QUATERNARY AMMONIUM SALT, PHENYL AMINES, PYRROLE, PYRIDINE, INDOLE AND ALKYL-SUBSTITUTED PYRROLES, PYRIDINES AND INDOLES.

Claim 3

In the process for the continuous preparation of C1-C5 hydrocarbyl aliphatic carboxylic acid esters of C2-C3 vicinal glycols by the catalytic liquid phase reaction of (a) an olefin corresponding in structure to the glycol moiety of said ester and selected from the group consisting of ethylene and propylene, (b) molecular oxygen and (c) a monobasic aliphatic hydrocarbyl carboxylic acid or 1-5 carbon atoms corresponding in structure to the acyl moiety of said ester; the catalyst for said reaction being a tellurium or selenium cation in combination with a halide anion, the combination being selected from the group consisting of tellurium cation plus bromide anion, selenium cation plus bromide anion and selenium cation plus chloride anion; said reaction being carried out within an oxidation zone containing a liquid phase reaction medium comprising reactants, catalyst and reaction products including the carboxylic acid esters and halogenated byproducts; wherein reactants are continuously introduced into the oxidation zone and at least a portion of the liquid phase reaction medium is continuously withdrawn, the withdrawn portion of the reaction medium being processed to recover carboxylic acid ester product, unconverted reactants and halogenated by-products and wherein the recovered unconverted reactants are recycled to the oxidation zone; the improvement which comprises: minimizing selectivity losses while maximizing rate of formation of carboxylic acid ester product by recycling at least a predominant portion of the halogenated by-products to the oxidation zone to provide a substantial portion of the halogen component of the catalyst system while conducting the reaction at a temperature exceeding 150*C. but not in excess of about 250*C. in the presence of at least 0.05 equivalent of a basicity control cation per gram-atom of halogen anion in the liquid phase reaction medium, said basicity control cation having, when in the form of a salt with the halide correSponding to that of the catalyst system, an activity coefficient of at least 0.40 and said basicity control cation not having a pH-reducing effect when in the form of a salt with the carboxylic acid reactant, the basicity control cation being selected from at least one member of the group consisting of the lanthanides, scandium, yttium, iron, cobalt, nickel, zinc, bismuth, chromium, manganese, molybdenum, copper, arsenic, antimony, alkyl amines, alkyl quaternary ammonium salts, phenyl amines, pyrrole, pyridine, indole and alkyl-substituted pyrroles, pyridines and indoles.

Claim 4

In the process for the continuous preparation of C1-C5 hydrocarbyl aliphatic carboxylic acid esters of C2-C3 vicinal glycols by the catalytic liquid phase reaction of (a) an olefin corresponding in structure to the glycol moiety of said ester and selected from the group consisting of ethylene and propylene, (b) molecular oxygen and (c) a monobasic aliphatic hydrocarbyl carboxylic acid or 1-5 carbon atoms corresponding in structure to the acyl moiety of said ester; the catalyst for said reaction being a tellurium or selenium cation in combination with a halide anion, the combination being selected from the group consisting of tellurium cation plus bromide anion, selenium cation plus bromide anion and selenium cation plus chloride anion; said reaction being carried out within an oxidation zone containing a liquid phase reaction medium comprising reactants, catalyst and reaction products including the carboxylic acid esters and halogenated byproducts; wherein reactants are continuously introduced into the oxidation zone and at least a portion of the liquid phase reaction medium is continuously withdrawn, the withdrawn portion of the reaction medium being processed to recover carboxylic acid ester product, unconverted reactants and halogenated by-products and wherein the recovered unconverted reactants are recycled to the oxidation zone; the improvement which comprises: minimizing selectivity losses while maximizing rate of formation of carboxylic acid ester product by recycling at least a predominant portion of the halogenated by-products to the oxidation zone to provide a substantial portion of the halogen component of the catalyst system while conducting the reaction at a temperature exceeding 150*C. but not in excess of about 250*C. in the presence of at least 0.05 equivalent of a basicity control cation per gram-atom of halogen anion in the liquid phase reaction medium, said basicity control cation having, when in the form of a salt with the halide correSponding to that of the catalyst system, an activity coefficient of at least 0.40 and said basicity control cation not having a pH-reducing effect when in the form of a salt with the carboxylic acid reactant, the basicity control cation being selected from at least one member of the group consisting of the lanthanides, scandium, yttium, iron, cobalt, nickel, zinc, bismuth, chromium, manganese, molybdenum, copper, arsenic, antimony, alkyl amines, alkyl quaternary ammonium salts, phenyl amines, pyrrole, pyridine, indole and alkyl-substituted pyrroles, pyridines and indoles.

Claim 5

In the process for the continuous preparation of C1-C5 hydrocarbyl aliphatic carboxylic acid esters of C2-C3 vicinal glycols by the catalytic liquid phase reaction of (a) an olefin corresponding in structure to the glycol moiety of said ester and selected from the group consisting of ethylene and propylene, (b) molecular oxygen and (c) a monobasic aliphatic hydrocarbyl carboxylic acid of 1-5 carbon atoms corresponding in structure to the acyl moiety of said ester; the catalyst for said reaction being a tellurium or selenium cation in combination with a halide anion, the combination being selected from the group consisting of tellurium cation plus bromide anion, selenium cation plus bromide anion and selenium cation plus chloride anion; said reaction being carried out within an oxidation zone containing a liquid phase reaction medium comprising reactants, catalyst and reaction products including the carboxylic acid esters and halogenated byproducts; wherein reactants are continuously introduced into the oxidation zone and at least a portion of the liquid phase reaction medium is continuously withdrawn, the withdrawn portion of the reaction medium being processed to recover carboxylic acid ester product, unconverted reactants and halogenated by-products and wherein the recovered unconverted reactants are recycled to the oxidation zone; the improvement which comprises: minimizing selectivity losses while maximizing rate of formation of carboxylic acid ester product by recycling at least a predominant portion of the halogenated by-products to the oxidation zone to provide a substantial portion of the halogen component of the catalyst system while conducting the reaction at a temperature exceeding 150*C. but not in excess of about 250*C. in the presence of at least 0.05 equivalent of a basicity control cation per gram-atom of halogen anion in the liquid phase reaction medium, said basicity control cation having, when in the form of a salt with the halide corresponding to that of the catalyst system, an activity coefficient of at least 0.40 and said basicity control cation not having a pH-reducing effect when in the form of a salt with the carboxylic acid reactant, the basicity control cation being selected from at least one member of the group consisting of alkyl amines, alkyl quaternary ammonium salts, phenyl amines, pyrrole, pyridine, indole and alkyl-substituted pyrroles, pyridines and indoles.

Claim 6

In the process for the continuous preparation of C1-C5 hydrocarbyl aliphatic carboxylic acid esters of C2-C3 vicinal glycols by the catalytic liquid phase reaction of (a) an olefin corresponding in structure to the glycol moiety of said ester and selected from the group consisting of ethylene and propylene, (b) molecular oxygen and (c) a monobasic aliphatic hydrocarbyl carboxylic acid of 1-5 carbon atoms corresponding in structure to the acyl moiety of said ester; the catalyst for said reaction being a tellurium or selenium cation in combination with a halide anion, the combination being selected from the group consisting of tellurium cation plus bromide anion, selenium cation plus bromide anion and selenium cation plus chloride anion; said reaction being carried out within an oxidation zone containing a liquid phase reaction medium comprising reactants, catalyst and reaction products including the carboxylic acid esters and halogenated byproducts; wherein reactants are continuously introduced into the oxidation zone and at least a portion of the liquid phase reaction medium is continuously withdrawn, the withdrawn portion of the reaction medium being processed to recover carboxylic acid ester product, unconverted reactants and halogenated by-products and wherein the recovered unconverted reactants are recycled to the oxidation zone; the improvement which comprises: minimizing selectivity losses while maximizing rate of formation of carboxylic acid ester product by recycling at least a predominant portion of the halogenated by-products to the oxidation zone to provide a substantial portion of the halogen component of the catalyst system while conducting the reaction at a temperature exceeding 150*C. but not in excess of about 250*C. in the presence of at least 0.05 equivalent of a basicity control cation per gram-atom of halogen anion in the liquid phase reaction medium, said basicity control cation having, when in the form of a salt with the halide corresponding to that of the catalyst system, an activity coefficient of at least 0.40 and said basicity control cation not having a pH-reducing effect when in the form of a salt with the carboxylic acid reactant, the basicity control cation being selected from at least one member of the group consisting of alkyl amines, alkyl quaternary ammonium salts, phenyl amines, pyrrole, pyridine, indole and alkyl-substituted pyrroles, pyridines and indoles.

Claim 7

In the process for the continuous preparation of C1-C5 hydrocarbyl aliphatic carboxylic acid esters of C2-C3 vicinal glycols by the catalytic liquid phase reaction of (a) an olefin corresponding in structure to the glycol moiety of said ester and selected from the group consisting of ethylene and propylene, (b) molecular oxygen and (c) a monobasic aliphatic hydrocarbyl carboxylic acid of 1-5 carbon atoms corresponding in structure to the acyl moiety of said ester; the catalyst for said reaction being a tellurium or selenium cation in combination with a halide anion, the combination being selected from the group consisting of tellurium cation plus bromide anion, selenium cation plus bromide anion and selenium cation plus chloride anion; said reaction being carried out within an oxidation zone containing a liquid phase reaction medium comprising reactants, catalYst and reaction products including the carboxylic acid esters and halogenated by-products, wherein reactants are continuously introduced into the oxidation zone and at least a portion of the liquid phase reaction medium is continuously withdrawn, the withdrawn portion of the reaction medium being processed to recover carboxylic acid ester product, unconverted reactants and halogenated by-products and wherein the recovered unconverted reactants are recycled to the oxidation zone; the improvement which comprises: minimizing selectivity losses while maximizing rate of formation of carboxylic acid ester product by recycling at least a predominant portion of the halogenated by-products to the oxidation zone to provide a substantial portion of the halogen component of the catalyst system while conducting the reaction at a temperature exceeding 150*C. but not in excess of about 250*C. in the presence of at least 0.05 equivalent of a basicity control cation per gram-atom of halogen anion in the liquid phase reaction medium, said basicity control cation having, when in the form of a salt with the halide corresponding to that of the catalyst system, an activity coefficient of at least 0.40 and said basicity control cation not having a pH-reducing effect when in the form of a salt with the carboxylic acid reactant, the basicity control cation being selected from at least one member of the group consisting of magnesium, zinc, calcium, manganese, nickel, cobalt, cerium, arsenic, antimony, iron, chromium, molybdenum, scandium, yttrium, bismuth and copper.

Claim 8

In the process for the continuous preparation of C1-C5 hydrocarbyl aliphatic carboxylic acid esters of C2-C3 vicinal glycols by the catalytic liquid phase reaction of (a) an olefin corresponding in structure to the glycol moiety of said ester and selected from the group consisting of ethylene and propylene, (b) molecular oxygen and (c) a monobasic aliphatic hydrocarbyl carboxylic acid of 1-5 carbon atoms corresponding in structure to the acyl moiety of said ester; the catalyst for said reaction being a tellurium or selenium cation in combination with a halide anion, the combination being selected from the group consisting of tellurium cation plus bromide anion, selenium cation plus bromide anion and selenium cation plus chloride anion; said reaction being carried out within an oxidation zone containing a liquid phase reaction medium comprising reactants, catalYst and reaction products including the carboxylic acid esters and halogenated by-products, wherein reactants are continuously introduced into the oxidation zone and at least a portion of the liquid phase reaction medium is continuously withdrawn, the withdrawn portion of the reaction medium being processed to recover carboxylic acid ester product, unconverted reactants and halogenated by-products and wherein the recovered unconverted reactants are recycled to the oxidation zone; the improvement which comprises: minimizing selectivity losses while maximizing rate of formation of carboxylic acid ester product by recycling at least a predominant portion of the halogenated by-products to the oxidation zone to provide a substantial portion of the halogen component of the catalyst system while conducting the reaction at a temperature exceeding 150*C. but not in excess of about 250*C. in the presence of at least 0.05 equivalent of a basicity control cation per gram-atom of halogen anion in the liquid phase reaction medium, said basicity control cation having, when in the form of a salt with the halide corresponding to that of the catalyst system, an activity coefficient of at least 0.40 and said basicity control cation not having a pH-reducing effect when in the form of a salt with the carboxylic acid reactant, the basicity control cation being selected from at least one member of the group consisting of magnesium, zinc, calcium, manganese, nickel, cobalt, cerium, arsenic, antimony, iron, chromium, molybdenum, scandium, yttrium, bismuth and copper.

Claim 9

In the process for the continuous preparation no C1-C5 hydrocarbyl aliphatic carboxylic acid esters of C2-C3 vicinal glycols by the catalytic liquid phase reaction of (a) an olefin corresponding in structure to the glycol moiety of said ester and selected from the group consisting of ethylene and propylene, (b) molecular oxygen and (c) a monobasic aliphatic hydrocarbyl carboxylic acid of 1-5 carbon atoms corresponding in structure to the acyl moiety of said ester; the catalyst for said reaction being a tellurium or selenium cation in combination with a halide anion, the combination being selected from the group consisting of tellurium cation plus bromide anion, selenium cation plus bromide anion and selenium cation plus chloride anion; said reaction being carried out within an oxidation zone containing a liquid phase reaction medium comprising reactants, catalyst and reaction products including the carboxylic acid esters and halogenated byproducts; wherein reactants are continuously introduced into the oxidation zone and at least a portion of the liquid phase reaction medium is continuously withdrawn, the withdrawn portion of the reaction medium being processed to recover carboxylic acid ester product, unconverted reactants and halogenated by-products and wherein the recovered unconverted reactants are recycled to the oxidation zone; the improvement which comprises: minimizing selectivity losses while maximizing rate of formation of carboxylic acid ester product by recycling at least a predominant portion of the halogenated by-products to the oxidation zone to provide a substantial portion of the halogen component of the catalyst system while conducting the reaction at a temperature exceeding 150*C. but not in excess of about 250*C. in the presence of at least 0.05 equivalent of a basicity control cation per gram-atom of halogen anion in the liquid phase reaction medium, said basicity control cation having, when in the form of a salt with the halide corresponding to that of the catalyst system, an activity coefficient of at least 0.40 and said basicity control cation not having a pH-reducing effect when in the form of a salt with the carboxylic acid reactant, the basicity control cation being selected from at least one member of the group consisting of zinc, manganese, nickel, cobalt, cerium, arsenic, anTimony, iron, chromium, molybdenum, scandium, yttrium, bismuth and copper.

Claim 10

In the process for the continuous preparation no C1-C5 hydrocarbyl aliphatic carboxylic acid esters of C2-C3 vicinal glycols by the catalytic liquid phase reaction of (a) an olefin corresponding in structure to the glycol moiety of said ester and selected from the group consisting of ethylene and propylene, (b) molecular oxygen and (c) a monobasic aliphatic hydrocarbyl carboxylic acid of 1-5 carbon atoms corresponding in structure to the acyl moiety of said ester; the catalyst for said reaction being a tellurium or selenium cation in combination with a halide anion, the combination being selected from the group consisting of tellurium cation plus bromide anion, selenium cation plus bromide anion and selenium cation plus chloride anion; said reaction being carried out within an oxidation zone containing a liquid phase reaction medium comprising reactants, catalyst and reaction products including the carboxylic acid esters and halogenated byproducts; wherein reactants are continuously introduced into the oxidation zone and at least a portion of the liquid phase reaction medium is continuously withdrawn, the withdrawn portion of the reaction medium being processed to recover carboxylic acid ester product, unconverted reactants and halogenated by-products and wherein the recovered unconverted reactants are recycled to the oxidation zone; the improvement which comprises: minimizing selectivity losses while maximizing rate of formation of carboxylic acid ester product by recycling at least a predominant portion of the halogenated by-products to the oxidation zone to provide a substantial portion of the halogen component of the catalyst system while conducting the reaction at a temperature exceeding 150*C. but not in excess of about 250*C. in the presence of at least 0.05 equivalent of a basicity control cation per gram-atom of halogen anion in the liquid phase reaction medium, said basicity control cation having, when in the form of a salt with the halide corresponding to that of the catalyst system, an activity coefficient of at least 0.40 and said basicity control cation not having a pH-reducing effect when in the form of a salt with the carboxylic acid reactant, the basicity control cation being selected from at least one member of the group consisting of zinc, manganese, nickel, cobalt, cerium, arsenic, anTimony, iron, chromium, molybdenum, scandium, yttrium, bismuth and copper.

Claim 11

A process in accordance with claim 5 wherein the basicity control cation is cobalt.

Claim 12

A process in accordance with claim 5 wherein the catalyst combination is tellurium cation plus a bromide anion.

Claim 13

A process in accordance with claim 6 wherein the catalyst combination is tellurium cation plus bromide anion.

Claim 14

A process in accordance with claim 5 wherein the olefin is ethylene.

Claim 15

A process in accordance with claim 5 wherein the olefin is ethylene and the carboxylic acid is acetic acid.

Claim 16

A process in accordance with claim 5 wherein the reaction temperature is in excess of 155*C. but not in excess of about 240*C.

Claim 17

A process in accordance with claim 6 wherein reaction temperature is in excess of 155*C. but not in excess of about 240*C.

Claim 18

A process in accordance with claim 5 wherein the basicity control cation is employed in an amount of at least 0.2 equivalent of basicity control cation per gram-atom of total halogen present in the liquid phase reaction medium.

Claim 19

A process in accordance with claim 5 wherein the amount of basicity control cation employed is between about 0.2 equivalent per gram-atom of total halogen and about 3.0 equivalents of basicity control cation per gram-atom of total halogen.

Claim 20

A process in accordance with claim 5 wherein the amount of basicity control cation employed is between about 0.5 equivalent per gram-atom of total halogen and about 1.5 equivalents of basicity control cation per gram-atom of total halogen.

Claim 21

A process in accordance with claim 5 wherein the olefin is ethylene; the carboxylic acid is acetic acid; the reaction temperature is in excess of 155*C. but not in excess of about 240*C.; the catalyst combination is tellurium employed in an amount between 0.4 and 3.0 wt. % of the liquid phase reaction medium plus bromine employed in an amount between 5 and 20 gram-atoms of bromine per gram-atom of tellurium; and, the amount of basicity control cation employed is between 0.5 and 1.5 equivalents of basicity control cation per gram-atom of total halogen within the liquid phase reaction medium.

Claim 22

A process in accordance with claim 5 wherein the olefin is propylene; the carboxylic acid is acetic acid; the reaction temperature is in excess of 155*C. but not in excess of about 240*C,; the catalyst combination is tellurium employed in an amount between 0.4 and 3.0 wt. % of the liquid phase reaction medium plus bromine employed in an amount between 5 and 20 gram-atoms of bromine per gram-atom of tellurium; and, the amount of basicity control cation employed is between 0.5 and 1.5 equivalents of basicity control cation per gram-atom of total halogen within the liquid phase reaction medium.

Claim 23

A process in accordance with claim 3 wherein the catalyst combination is tellurium cation plus a bromide anion.

Claim 24

A process in accordance with claim 3 wherein the olefin is ethylene.

Claim 25

A process in accordance with claim 3 wherein the olefin is ethylene and the carboxylic acid is acetic acid.

Claim 26

A process in accordance with claim 3 wherein the reaction temperature is in excess of 155*C. but not in excess of about 240*C.

Claim 27

A process in accordance with claim 3 wherein the basicity control cation is employed in an amount of at least 0.2 equivalent of basicity control cation per gram-atom of total halogen present in the liquid phase reaction medium.

Claim 28

A process in accordance with claim 3 wherein the amount of basicity control cation employed is between about 0.2 equivalent per gram-atom of total halogen and about 3.0 equivalents of basicity control cation per gram-atom of total halogen.

Claim 29

A process in accordance with claim 3 wherein the amount of basicity control cation employed is between aboUt 0.5 equivalent per gram-atom of total halogen and about 1.5 equivalents of basicity control cation per gram-atom of total halogen.

Claim 30

A process in accordance with claim 3 wherein the olefin is ethylene; the carboxylic acid is acetic acid; the reaction temperature is in excess of 155*C. but not in excess of about 240*C,; the catalyst combination is tellurium employed in an amount between 0.4 and 3.0 wt. % of the liquid phase reaction medium plus bromine employed in an amount between 5 and 20 gram-atoms of bromine per gram-atom of tellurium; and, the amount of basicity control cation employed is between 0.5 and 1.5 equivalents of basicity control cation per gram-atom of total halogen within the liquid phase reaction medium.

Claim 31

A process in accordance with claim 3 wherein the olefin is propylene; the carboxylic acid is acetic acid; the reaction temperature is in excess of 155*C. but not in excess of about 240*C., the catalyst combination is tellurium employed in an amount between 0.4 and 3.0 wt. % of the liquid phase reaction medium plus bromine employed in an amount between 5 and 20 gram-atoms of bromine per gram-atom of tellurium; and, the amount of basicity control cation employed is between 0.5 and 1.5 equivalents of basicity control cation per gram-atom of total halogen within the liquid phase reaction medium.