FORM 2
THE PATENTS ACT 1970
(39 of 1970)
AND
The Patents Rules, 2003
COMPLETE SPECIFICATION
(See section 10 and rulel3)
1. TITLE OF THE INVENTION:
"PROCESS FOR TERMINAL DIHALOALKANE"
2. APPLICANT:
(a) NAME: Omkar Speciality Chemicals Limited
(b) NATIONALITY: Indian Company incorporated under the
Companies Act, 1956
(c) ADDRESS: B-34, MIDC, Badlapur (East), Dist -Thane-421503,
Maharashtra, India.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in which it is to be formed.

TECHNICAL FIELD:
The present invention relates to a method of synthesizing Terminal dihaloalkane of formula (1) by reacting alkane dihalide with metal iodides in presence of catalytic amounts of tetra butyl ammonium iodide in polar solvent or mixtures of polar solvents and isolation of the same with more than 99% purity.
BACKGROUND AND PRIOR ART:
Terminal dihaloalkanes are produced by the action of sodium arsenate on aliphatic trihaloalkane as described in Organic Syntheses, Coll. Vol. 1, p.358 (1941) wherein iodoform is reacted with sodium arsenate to obtain methylene diiodide.
In an article titled "Synthesis of methylene iodide", described in J. Chem. Soc, 119,
1048, (1921), methylene chloride and Nal in acetone are heated for lOh to obtain
Diiodomethane
J. Chinese Chem. Soc. 34, 325-328 (1987) discloses reaction of diiodomethane and
dichloromethane with molecular iodine in presence of aluminium powder as catalyst to
give chloroiodomethane.
CN102020529 and CN102020528 deal with preparation of Diiodomethane and chloroiodomethane wherein sodium iodide, careen and DMF are used in varying quantities to obtain desired product. However, the above mentioned processes are not commercially viable and are costly also. Further, the above patent application fails to mention the preparation of terminal dihaloalkanes with carbon chain length 1-12.
Thus a cursory review of the prior arts fails to mention the preparation of terminal dihaloalkanes with carbon chain length 1-12 with good yield and purity. Also, the prior art processes results in side products which need to be separated from the desired product before proceeding with the same. Any improvement in the area of yield and purity of the desired product is important for a synthesis as it invariably deals with the process economics.

Hence, the objective of the present invention is to provide simple method for the preparation of Terminal dihaloalkanes with carbon chain length 1-12 which is economically and commercially viable.
SUMMARY OF INVENTION:
In accordance with the above, the present invention discloses a method of synthesizing Terminal dihaloalkane of formula (1).
X1(CH2)nX2 (1)
Wherein,
Xi = X2 = Br,I
X, X2 = Cl,Br,I
n = l-12
Terminal dihaloalkanes according to the present invention are prepared by reacting metal
iodides (2) with alkane dihalide (3) in presence of polar solvent or mixtures of polar
solvents which include but are not limited to N, N-dimethyl formamide, ethanol and
acetone.
A(I)m (2)
Wherein A = alkali earth metal or the metals capable of forming bond with iodine in +1 and +3 oxidation state which includes but are not limited to Cu+1, Al+3, P+3 and m = 1 or 3.
X2(CH2)n- (3)
Wherein X = CI, Br and n=l-12
DETAIL DESCRIPTION OF THE INVENTION:
Accordingly, the present invention discloses a simple, efficient method of synthesizing Terminal dihaloalkane as shown in scheme 1. Terminal dihaloalkane finds its applicability in simmons-smith reaction; in cross linking polymerization, serves as source of methylene group in organic transformations. They are also used as flame retardants, fire extinguisher, refrigerants, propellants, solvents, and pharmaceuticals.

In a preferred embodiment, the process of present invention comprises reaction of metal iodides and alkane dichloride in the presence of polar solvent or mixtures of solvents which include but are not limited to N, N-dimethyl formamide, ethanol, and acetone. The invention utilizes catalytic amount of tetra butyl ammonium iodide as promoter to enhance the rate of reaction. The reaction can be carried in any reaction vessel suitable for the reaction and no special techniques are needed.
The method of synthesizing Terminal dihaloalkane according to the invention is shown in scheme 1.

Where,
A = alkali earth metal or the metals capable of forming bond with iodine in +1 and +3
oxidation state which includes but are not limited to Cu+1, Al+3, P+3 and m = 1 or 3.
X = Cl,Brandn=l-12
X, = X2 = Br,I
Xi X2=Cl,Br,I
n=l-12
As depicted in scheme (1), in one preferred embodiment, Sodium iodide and Methylene dichloride, and catalytic quantity of quaternary ammonium salt are added to the reactor. Polar solvent or mixture of polar solvents which includes but are not limited to N, N-dimethyl formamide, ethanol, acetone is added to the above reactor in the temperature range of 25-50°C, more preferably between 35-40°C. The reaction mass is heated gradually in the temperature range of 125-160°C most preferably in the range of 135-145°C. Care has to be taken while maintaining reaction temperature above 160oC as iodine liberates from the reaction mass. After attaining appropriate temperature, the reaction is maintained for l-3h. After completion of reaction, necessary work up is carried to isolate the product of present invention.
According to the present invention, the product in this case, Diiodomethane, is distilled in presence of copper wires to improve color of product, which forms another aspect of the

invention. The product obtained is with a yield of 70-75 % with purity not less than 99%. The remaining unreacted source of halide is recycled and reused.
When Dichloro alkanes of C1-C12 are used reaction, the reaction time varies from 2-36h and the yield varies from 75-50%.
In another preferred embodiment according to the invention, Cu (1) iodide, is taken as iodine source to carry out the above reaction.
In a further embodiment, Al+3 iodide is used as iodine source to conduct the above reaction. In yet another embodiment, the invention may be performed with P+3 iodide as the source of iodine.
In another preferred embodiment, Sodium iodide and ethylene dichloride, and catalytic quantity of quaternary ammonium salt are added to the reactor. Polar solvent or mixtures of polar solvents selected from the group consisting of N, N-dimethyl formamide, ethanol, acetone is added to the above reactor in the temperature range of 25-50oC, more preferably between 35-40oC. The reaction mass is heated gradually in the temperature range of 125-160oC most preferably in the range of 135-145oC. After attaining appropriate temperature, the reaction is maintained for l-3h. After completion of reaction, necessary work up is carried to isolate the product of present invention. The product obtained in this case, Diiodoethane is distilled in presence of copper wires to improve color of product. Product is isolated with a yield of 70-75 % with purity not less than 99%. The remaining unreacted source of halide is recycled and reused.
The following examples, which include preferred embodiments, will serve to illustrate the practice of this invention, it being understood that the particulars shown are by way of example and for purpose of illustrative discussion of preferred embodiments of the invention.

Examples Example 1
In a 5L reactor 1kg sodium iodide and 0.28kg methylene dichloride and catalytic amount of tetra butyl ammonium iodide was added. 0.8L N, N-dimethyl formamide was added and temperature of the reaction was increased to 140°C and reaction was maintained in the range of 135-145°C for 2h. After reaction completion 1.6L DI water was added layers were separated. Organic layer was washed with 300mL of 10% sodium thiosulphate solution. Crude product was distilled in presence of copper wire to obtain 662gm of Diiodomethane with 99% purity.
Example 2
In a 5L reactor 1kg sodium iodide and 0.28kg methylene dichloride. 0.8L N, N-dimethyl formamide was added and temperature of the reaction was increased to 140°C and reaction was maintained in the range of 135-145°C for 6h. After reaction completion 1.6L DI water was added layers were separated. Organic layer was washed with 300mL of 10% sodium thiosulphate solution. Crude product was distilled in presence of copper wire to obtain 609gm of Diiodomethane with 99% purity.
From the above, it is clear that the reaction period is less in case where catalyst is used and also the yield of the product is relatively poor.
Example 3
In a 5L reactor 1kg sodium iodide and 0.28kg methylene dichloride and catalytic amount of tetra butyl ammonium iodide was added. 0.8L N, N-dimethyl formamide was added and temperature of the reaction was increased to 140°C and reaction was maintained in the range of 135-145°C for 2h. After reaction completion 1.6L DI water was added layers were separated. Organic layer was washed with 300mL of 10% sodium thiosulphate solution. Crude product was distilled in absence of copper wire to obtain 650gm of Diiodomethane with 97% purity.
In the absence of copper wire we have observed liberation of iodine while distillation and color of product was brown due to free iodine present. Although the yield of crude was

almost comparable but yield and purity both are affected during distillation in the absence of copper wire.
Example 4
Series of experiments were carried by procedure described in Example 1 varying reaction time. The results obtained are summarized in the table given below:

Sr. no. Experiment no. Reaction time (h) Result (9)
1 1 1 500
2 2 2 662
3 3 4 661
4 4 6 662
5 5 8 660
From the above table it is clear that after end of 2hrs, the yield of product is almost constant.
Example 5
Series of experiments were carried by procedure described in Example 1 varying reaction
temperature. The results obtained are summarized in the table given below:

Sr. no. Experiment no. Reaction temperature (°C) Result (g)
1 1 105 265
2 2 125 574
3 3 135 662
4 4 145 636
4 4 155 486
5 5 165 221
Example 6
In a 5L reactor 1kg sodium iodide and 0. 0.35kg ethylene dichloride and catalytic amount of tetra butyl ammonium iodide was added. 0.84L N, N-dimethyl formamide was added and temperature of the reaction was increased to 140°C and reaction was maintained in

the range of 135-145°C for 2h. After reaction completion 1.6L DI water was added layers were separated. Organic layer was washed with 300mL of 10% sodium thiosulphate solution. Crude product was distilled in presence of copper wire to obtain 728 g of Diiodoethane with 99% purity.
Example 7
Similarly, series of experiments were carried out by reacting 1 mole of Dichloro alkane from C3-C12 using 2 moles of sodium iodide at similar experimental procedure described in Example 1. The results obtained are summarized in the table given below:

Sr. no. Reactant Result (g) Yield (%)

2 C3H6C12 210 70
3 C4H8C12 217 70
4 C5H10Cl2 224 69
4 C6H12C12 226 67
5 C7H14C12 229 65
6 C8H16C12 227 62
7 C9H18CI2 228 60
8 C10H2oCl2 225 57
9 C11H22CI2 216 53
10 C12H24CI2 211 ' 50
It is believed that a person skilled in the art can, based on the description herein; utilize the present invention to its fullest extent. The specific example as shown above is therefore to be construed as merely illustrative and not limitative.

WE CLAIM,
1. A process for synthesis of Terminal dihaloalkane of formula (1) comprising
reacting alkane dihalide (3) with metal iodides (2), characterized in that the
reaction is conducted in presence of catalytic quantity of quaternary ammonium
salt and in polar solvents or mixture of polar solvents at a temperature range of
125-160°C and distilling the terminal dihaloalkane in presence of copper wire to
obtain the product with a purity of greater than 99%.
X1(CH2)nX2
(Formula 1)
wherein, X1 = X2 = Br, I X1 X2 = Cl,Br,I n=l-12
2. The process according to claim 1, wherein the metal iodides are of formula A(I) m wherein A = alkali earth metal or the metals capable of forming bond with iodine in +1 and +3 oxidation state, selected from the group consisting of Cu+1, Al+3,P+3andm = lor3.
3. The process according to claim 1, wherein the alkane dihalide is of formula X2(CH2) n,
wherein, X = CI, Br and n = l-12
4. The process according to claim 1, wherein the polar solvent is selected from the group consisting of N, N-Dimethyl formamide, ethanol, acetone or mixtures thereof.
5. The process according to claim 1, wherein the distillation of the product is essentially carried in presence of copper wire to improve color of product.
6. The process according to claim 1, wherein the solvent addition is done at a temperature range of 25-50°C.

7. The process according to claim 1, wherein the reaction is maintained at a temperature range of 135-145°C for 1 to 36 hrs.
8. The process according to any one of the preceding claims, wherein the yield obtained varies from 50-75% depending upon starting material taken.