FORM 2
THE PATENT ACT, 1970
(39 OF 1970)
&
THE PATENTS RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
1. TITLE OF THE INVENTION:
EFFICIENT IODINATION OF ALKANE
2. APPLICANT
a) NAME : OMKAR SPECIALITY CHEMICALS LTD.
b) NATIONALITY : INDIAN
c) ADDRESS : B-34, M.I.D.C. BADLAPUR (E),
DIST-THANE, PIN-421503, MAHARASHTRA, INDIA
The following specification particularly describes the invention and the manner in which it is to be performed.

EFFICIENT IODINATION OF ALKANE FIELD OF INVENTION:
The present invention relates to a high yielding and short duration process for preparing diiodoalkane. More particularly it relates to reacting dihaloalkane with metal iodide in presence of catalyst tetra butyl ammonium iodide.
BACKGROUND OF INVENTION:
Below are the few reported processes for diiodoalkane preparation.
As per the process described in Organic Syntheses, Coll. Vol. 1, p.358 (1941)
methylene diiodide is obtained by treating CHI3 with sodium arsenate.
10 hrs heating of methylene chloride and Nal in acetone is necessary for the process
described in J.'Chem. Soc, 119, 1048, (1921).
CN102020529 described a process for preparing Diiodomethane where the ratios of
reactants and solvents are varied for obtaining the desired product. Still it needs 6-8
hrs heating and lengthy processing for isolation of Diiodomethane.
Along with generation of side products requiring extensive purification, prior art
processes are not commercially viable and are costly also. Thus, improvement in
yield and purity are the important aspects in this area which make the production
economically viable.
SUMMARY OF INVENTION:
Present invention provides a process for preparing diiodoalkane by reacting dihaloalkane with metal iodide in presence of catalyst tetra butyl ammonium iodide. Dihaloalkanes ranges from C1 to C12 alkanes. The preferable solvent for this process is polar solvent or their mixture. Temperature ranging from 135°C to 140°C is

preferred. Water is added to the final mixture and product is obtained in organic layer which is washed with sodium thiosulphate and distilled in presence of copper wire to give high purity diiodoalkane.
DETAIL DESCRIPTION OF INVENTION:
Accordingly, the present invention discloses a simple, efficient process for preparing diiodoalkane. Diiodoalkane are useful 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.
Without restricting to any particular sequence the process can be carried by reacting dihaloalkane with metal iodide in presence of catalyst tetra butyl ammonium iodide. Dihaloalkanes ranges from rom C1 to C12 alkanes having chlorine or bromine halogen atoms. Preferably polar solvent or their mixtures are suitably employed for this process. More preferably solvents like N, N-dimethyl formamide, ethanol and acetone are suitable.
The reactants and catalyst are taken in a suitable reaction vessel and then the solvent/s is added to it at the temperature ranging from 25° to 50° and more preferably at 35°to 40°C. This reaction mixture is heated within the temperature range of 125° to 160°C and most preferably in the range of 135-145°C. After continuing heating for 2-3 hours, water is added to the final mixture to get phase separation, aqueous layer is discarded and product is obtained in organic layer which is washed with sodium thiosulphate and distilled in presence of copper wire to give high purity diiodoalkane.
In one embodiment methylene dichloride, sodium iodide and catalyst tetra butyl ammonium iodide are taken in a suitable reaction vessel and then the solvent/s is

f
added to it at the temperature ranging from 25° to 50° and more preferably at 35°to 40°C. This reaction mixture is heated within the temperature range of 125° to 160°C and most preferably in the range of 135-145°C. After continuing heating for 2-3 hours, water is added to the final mixture to get phase separation, aqueous layer is discarded and product is obtained in organic layer which is washed with sodium thiosulphate and distilled in presence of copper wire to give high purity diiodomethane.
In another embodiment ethylene chloride, sodium iodide and catalyst tetra butyl ammonium iodide are reacted in same manner and the final mixture is processed in similar way to obtain high purity Diiodoethane.
The process yields about 70-75 % diiodoalkane with purity not less than 99% Likewise other diiodoalkane in high purity are obtained by employing corresponding alkane in this process reaction. Also, copper iodide, phosphorus iodide and aluminum iodide are the alternative iodine sources usable in this process.
The present invention is further described with the help of the following example, which is given by way of illustration and should not be construed to limit the scope of the invention in any manner.
Example 1: Reaction using catalyst tetra butyl ammonium iodide and distillation in presence of copper wire
Methylene dichloride (0.28 kg), sodium iodide (1 kg) and catalytic amount of tetra butyl ammonium iodide was taken in a 5L reactor. N, N-dimethyl formamide (0.8 L) was added at 35°C and heated to 140°C and maintained in the range of 135-145°C for 2h. Water (1.6 L) was added to final reaction mixture and layers were separated. Organic layer washed with 10% sodium thiosulphate solution (300 mL) and crude product was distilled in presence of copper wire to obtain Diiodomethane. Yield: 662 gm

Purity: 99%
Example 2: Reaction using catalyst tetra butyl ammonium iodide and distillation in presence of copper wire
Ethylene dichloride (0.35 kg), sodium iodide (1 kg) and catalytic amount of tetra butyl ammonium iodide was taken in a 5L reactor, N, N-dimethyl formamide (0.84 L) was added at 35°C and heated to 140°C and maintained in the range of 135-145°C for 2h. Water (1.6 L) was added to final reaction mixture and layers were separated. Organic layer washed with 10% sodium thiosulphate solution (300 mL) and crude product was distilled in presence of copper wire to obtain Diiodoethane. Yield: 728 gm Purity: 99%
Example 3: Reaction without catalyst tetra butyl ammonium iodide and distillation in presence of copper wire
Procedure described in Example 1 was carried out without using catalyst tetra butyl ammonium iodide and (thus) increasing the heating upto 6hrs to obtain only 609 gm of Diiodomethane. Purity: 99%
Example 4: Reaction using catalyst tetra butyl ammonium iodide and distillation without using copper wire
Procedure described in Example 1 was carried but without using copper wire while distillation to obtain 97% Diiodomethane.
Example 5: Varying heating time

Procedure described in Example 1 was carried for 5 similar experiments but with varying heating time for each.

Heating time (hrs) Yield (gm)
1 500
2 662
4 661
6 662
8 660
Thus, two to three hours heating is sufficient to get maximum yield from this process.
Example 6: Varying heating time
Procedure described in Example 1 was carried for 5 similar experiments but with varying heating temperature for each.

Heating temperature (°C) Yield (gm)
105 265
125 574
135 662
145 636
155 482
165 221
Thus, heating within the temperature range of 135°C to 145° is sufficient to get maximum yield from this process.
Example 6: Varying heating time

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 Yield (gm) Yield (%)
1 C3H6CI2 210 70
2 C4H8C12 217 70
3 C5H10CI2 224 69
4 C6H12CI2 226 67
5 C7H14CI2 229 65
6 CgH]6Cl2 227 62
7 C9H18G2 228 60
8 C10H20C12 225 57
9 C11H22C12 216 53
10 C12H24C12 211 50

Claims:
1. A process for preparing diiodoalkane by reacting dihaloalkane with metal iodide in presence of catalyst tetra butyl ammonium iodide.
2. The process of claim 1, wherein dihaloalkane is reacted with metal iodide in polar solvent in presence of catalyst tetra butyl ammonium iodide.
3. The process of claim 1, wherein dihaloalkane is selected from Ci to C^ alkanes having chlorine or bromine halogen atoms.
4. The process of claim 1, wherein metal iodide is selected from copper iodide, phosphorus iodide and aluminum iodide.
5. The process of claim 1, wherein the reaction is maintained within the temperature range of 135°C-145°C for 2 to 3 hrs.
6. The process of claim 5, further comprising adding water to the final mixture; discarding aqueous layer; washing organic layer with sodium thiosulphate and carrying out distillation in presence of copper wire to get high purity diiodoalkane.