The present invention provides a process for preparation of substituted alkanols.

BACKGROUND OF THE INVENTION
The present invention provides a process for preparation of substituted alkanols. Substituted alkanols like fluorinated alcohol are useful as solvent for preparing a photoreceptor for a film or a recording layer for an information recording medium (such as an optical disk such as CD-R or DVD-R) capable of writing and/or reading information by a laser formed on a substrate.
Various methods are known in the art for the preparation of substituted alkanols. EP Patent App. No. 968989 provides a process for producing 2,2,3,3-tetrafluoro-1-propanol by reacting methanol with tetrafluoroethylene or hexafluoropropylene in the presence of an initiator at a pressure of about 0.2-1.2 MPa (2 to 12 Kg/cm2) and distilling the product after decomposing the remaining initiator contained in the reaction mixture.
EP Patent App. No. 967193 provides a method for producing tetrafluoropropanol by reacting methanol with tetrafluoroethylene or hexafluoropropylene in the presence of a free radical source at a pressure of about 0.2-1.2 MPa (2 to 12 Kg/cm2) and distilling the product in presence of a base.
The main disadvantage of the above processes is that the various methods used for decomposition of radical initiators makes the process lengthy and costly at industrial scale. Thus there is a need to develop an alternative process for the preparation of substituted alkanols.
Surprisingly, the inventors of the present invention found that substituted alkanols can be prepared in good yield by using a series of reactors connected to each other in a specific manner.

OBJECT OF THE INVENTION
The object of the present invention is to provide an alternative and cost effective process for the preparation of a compound of formula 1,

Formula 1
wherein R1, R2, R3 and R4 is selected independently from fluorine, hydrogen, methyl, fluoromethyl; and n is any number selected from 1 to 10.

SUMMARY OF THE INVENTION
The present invention provides a continuous process for preparation of a compound of formula 1,

Formula 1
wherein R1, R2, R3 and R4 is selected independently from fluorine, hydrogen, methyl, fluoromethyl; and n is any number selected from 1 to 10.
comprising the steps of:
a) adding C1-10 alkanols and a radical initiator in a reactor apparatus;
b) adding a compound of formula 2,

Formula 2
in the reactor apparatus to obtain the compound of formula 1; and
c) isolating the compound of formula 1.

BRIEF DESCRIPTION OF DRAWING
Figure 1 depicts a reactor apparatus of the present invention. The reactor apparatus consists of ‘n’ number of reactors R1, R2, R3, R4 respectively, connected in a series with subsequent reactor. The reactor apparatus additionally has Pressure Gauges (1), Valves (2), Metal Condensers (3), container of compound of formula 2 (C1), and product collection tank (C2). Each reactor is further equipped with an Inlet (4), and Vent (5).

DETAILED DESCRIPTION OF THE INVENTION
As used herein, fluoromethyl is selected from monofluoromethyl, difluoromethyl and trifluoromethyl. It is preferred that only one of the R1, R2, R3 and R4 is fluoromethyl.
As used herein, the reactor apparatus consists of ‘n’ number of reactors connected in a series, wherein vent of each reactor is connected to the inlet of subsequent reactor. The ‘n’ is preferably 2-8.
As used herein, the process of the present invention is either a batch process or a continuous process.
In a batch process, the unreacted compound of formula 2 in last reactor is quenched using bromine scrubber at a temperature selected in the range of 0 to 30°C.
In a continuous process, the unreacted compound of formula 2 is recycled back to the first reactor.
In a continuous process, the reaction apparatus consists of n number of reactors connected in series, wherein vent of each reactor is connected to the inlet of subsequent reactor and the vent of last reactor is connected to inlet of first reactor.
The reaction apparatus results in transfer of excess of compound of formula 2 from each reactor to next reactor and also from last reactor to first reactor. This particular reactor setup, results in consumption of excess of compound of formula 2 from each reactor in subsequent reactors.
It also results in lowering dimer and trimer impurity which may form if excess of compound of formula 2 present in the system is not consumed effectively.
As used herein, the dimer impurity has a formula as shown below:

Dimer impurity
wherein R1, R2, R3 and R4 is selected independently from fluorine, hydrogen, methyl and fluoromethyl; and n is any number selected from 1 to 10.
In an embodiment, the compound of formula 1 is obtained with a dimer impurity below 2.5%.
In another embodiment, the compound of formula 1 is obtained with a dimer impurity below 1.0%. In still another embodiment, the compound of formula 1 is obtained with a dimer impurity of formula 3 below 0.1%.
In an embodiment, the compound of formula 1 is obtained with a dimer impurity in the range of 0.1 to 2.5%.
As used herein, the trimer impurity has a formula as shown below:

Trimer impurity
wherein R1, R2, R3 and R4 is selected independently from fluorine, hydrogen, methyl, fluoromethyl; and n is any number selected from 1 to 10.
In an embodiment, the compound of formula 1 is obtained with a trimer impurity below 1%,
In another embodiment, the compound of formula 1 is obtained with a trimer impurity below 0.05%.
In an embodiment, the compound of formula 1 is obtained with a trimer impurity in the range of 0 to 1%.
As used herein, the radical initiator is a peroxide of the following formula 3.
R5—O—O—Y—R6
Formula 3
wherein Y is carbon or a keto group. R5 is a C1—20 aliphatic hydrocarbon group, and R6 is a C1—20 aliphatic hydrocarbon group, or an aromatic hydrocarbon group.
The C1—20 aliphatic hydrocarbon group is preferably saturated aliphatic hydrocarbon group, which may, for example, be an alkyl group, a cycloalkyl group or a cycloalkylaryl group, and particularly preferred is an alkyl group. Further, the aromatic hydrocarbon group may, for example, be a phenyl group or a phenyl group having a substituent.
Specific examples of the alkyl peroxide of the formula 3 include di-tert-butyl peroxide, tert-butyl peroxy-2-ethyl hexanoate, tert-butyl proxy isopropyl carbonate and tert-butyl cumyl peroxide. Among them, tert-butyl peroxy-2-ethyl hexanoate is most preferred radical initiator used in the present invention.
Further UV radiations, heat, an azo type initiator or a photo radical initiator may be used either alone or in combination with the peroxide.
The compound of formula 2 is reacted with alkanol at a pressure selected in the range of 0 to 12Kg/cm2. In a preferred embodiment, the reaction is carried out at pressure of 4Kg/cm2.
As used herein, alkanol is selected in a range of 8 to 13 mole equivalent with respect to formula 2. In a preferred embodiment, 12 mole equivalents of alkanol are used.
As used herein, bromine is selected in a range of 0.3 to 0.9 mole equivalents with respect to formula 2. In a preferred embodiment, 0.5 equivalents of bromine are used.
In an embodiment, the compound of formula 2 and 3 are reacted at a temperature selected in the range of 40 to 60°C.
In an embodiment, reaction mass was flushed with nitrogen gas for at least 10 to 15 minutes at a temperature selected in the range of 40 to 60°C.
The compound of formula 1 as prepared by the process of the present invention has a selectivity of at least 90% which tends to maximum conversion of reactant into desired product which also results in very high yield.
In an embodiment, the compound of formula 1 as prepared by the process of the present invention has a selectivity in the range of 90 to 98%.
In an embodiment, the compound of formula 1 is obtained with a purity of at least 95%. In another embodiment, the compound of formula 1 is obtained with a purity of at least 97%. In still another embodiment, the compound of formula 1 is obtained with a purity of at least 99%.
In an embodiment, the compound of formula 1 is obtained with a purity in the range of 95% to 99%.
In another embodiment, the compound of formula 1 is obtained with a yield of at least 75%. In still another embodiment, the compound of formula 1 is obtained with a yield of at least 90%.
In an embodiment, the compound of formula 1 is obtained with a yield in the range of 75% to 90%.
After reaction completion, the reaction mass was cooled to 30°C and unloaded from the reactor.
As used herein, the term “isolating” refers to the method used to isolate the compound from the reaction mixture. The isolation is carried out using any of the process consisting of extraction, distillation, filtration, decantation, washing, dryings or combination thereof.
In an embodiment the isolation of compound of formula 1 from the reaction mixture is performed using distillation at reduced pressure (300 mmHg to 40 mmHg) at 55-60°C.
In another embodiment, the isolation of compound of formula 1 from the reaction mixture is performed using distillation at reduced pressure (300 mmHg to 40 mm Hg) at 55-60°C followed by drying to remove excess water.
In another embodiment, distillation is performed without using any decomposing agents such as acid catalyst, reducing agent, UV irradiation or a base.
In a preferred embodiment, sodium sulphate, calcium sulphate, calcium chloride, silica, alumina and calcium oxide are used to remove moisture.
In an embodiment, the moisture content after drying is in the range of 0.01 to 0.5% w/w.
The completion of the reaction is monitored by gas chromatography (GC).
In an embodiment, the stream containing unreacted alkanols and compound of formula 2 from each reactor was passed through a condenser before passing to next reactor to condense alkanols. It allows only compound of formula 2 to pass to the next reactor.
Unless stated to the contrary, any of the words “comprising”, “comprises” and includes mean “including without limitation” and shall not be construed to limit any general statement that it follows to the specific or similar items or matters immediately following it.
Embodiments of the invention are not mutually exclusive, but may be implemented in various combinations. The described embodiments of the invention and the disclosed examples are given for the purpose of illustration rather than limitation of the invention as set forth in the appended claims.
The compound of formula 2 which is used herein as starting material can be prepared by any of the methods known in the art i.e., or can be obtained commercially.
The following example is given by way of illustration and therefore should not be construed to limit the scope of the present invention.
EXAMPLES
Example 1: Methanol (242g) and tert-butylperoxy-2-ethyl hexanoate (3.8g) as radical initiator were charged in reactor 1. The same quantity of methanol and radical initiator was charged into two separate reactors 2 & 3. Bromine (378g) was charged to another reactor 4. The reactors 1, 2, 3 & 4 were connected in such way that vent of each reactor is connected to inlet of subsequent reactor. The reactor 4 contains bromine which was used as scrubber and scrubber temperature was maintained at 0 to 30°C. The reaction mass of reactor 1, 2 & 3 was heated to 40 to 60°C and flushed with nitrogen gas for 10 to 15 minutes. After nitrogen gas flushing, tetrafluoroethylene (TFE) gas was purged into the reaction mass of reactor 1, 2 & 3 at 40 to 60°C. Progress of the reaction was monitored by GC analysis. After reaction completion, the reaction mass containing 2,2,3,3-tetrafluoro-1-propanol was cooled to 30°C and unloaded from the reactor. The unreacted tetrafluoroethylene was quenched using bromine scrubber. The unloaded mass was taken for product isolation by distillation and pure product was dried subsequently to obtain the title compound.
Yield: 75%,
Purity: 95% (by GC area)
Example 2: Methanol (242g) and tert-butylperoxy-2-ethyl hexanoate (3.8g) as radical initiator was charged in reactor 1. The same quantity of methanol and radical initiator was charged into two separate reactors 2 & 3. The reactors 1, 2 & 3 were connected in such way that vent of each reactor is connected to inlet of subsequent reactor and vent of reactor 3 is connected to inlet of reactor 1. The reaction mass was heated to 40 to 60°C and tetrafluoroethylene (TFE) gas was purged into the reaction mass of reactor 1. Progress of the reaction was monitored by GC analysis. The reaction mass containing 2,2,3,3-tetrafluoro-1-propanol was cooled to 30°C and unloaded from all the reactors continuously. The unloaded mass was taken for product isolation by distillation and pure product was dried subsequently to obtain the title compound. The unreacted TFE from third reactor was recycled back to reactor 1.
Yield: 90%,
Purity: 95% (by GC area)
Example 3: Methanol (242g) and tert-butylperoxy-2-ethyl hexanoate (3.8g) as radical initiator was charged in reactor 1. The same quantity of methanol and radical initiator was charged into three separate reactors 2, 3 & 4. The reactors 1, 2, 3 & 4 were connected (as shown in figure 1) in such way that vent of each reactor is connected to inlet of subsequent reactor and vent of reactor 4 is connected to inlet of reactor 1. The reaction mass was heated to 40 to 60°C and tetrafluoroethylene (TFE) gas was purged into the reaction mass of reactor 1. Progress of the reaction was monitored by GC analysis. The reaction mass containing 2,2,3,3-tetrafluoro-1-propanol was cooled to 30°C and unloaded from all the reactors continuously. The unloaded mass was taken for product isolation by distillation and pure product was dried subsequently to obtain the title compound. The unreacted TFE from fourth reactor was recycled back to reactor 1.
Yield: 93%,
Purity: 96% (by GC area)
Example 4: Methanol (242g) and di-tert-butyl peroxide (6.8g) as radical initiator was charged in reactor 1. The same quantity of methanol and radical initiator was charged into three separate reactors 2, 3 & 4. The reactors 1, 2, 3 & 4 were connected (as shown in figure 1) in such way that vent of each reactor is connected to inlet of subsequent reactor and vent of reactor 4 is connected to inlet of reactor 1. The reaction mass was heated to 40 to 60°C and tetrafluoroethylene (TFE) gas was purged into the reaction mass of reactor 1. Progress of the reaction was monitored by GC analysis. The reaction mass containing 2,2,3,3-tetrafluoro-1-propanol was cooled to 30°C and unloaded from all the reactors continuously. The unloaded mass was taken for product isolation by distillation and pure product was dried subsequently to obtain the title compound. The unreacted TFE from fourth reactor was recycled back to reactor 1.
Yield: 94%,
Purity: 97% (by GC area)

CLAIMS:WE CLAIM:
1. A process for preparation of a compound of formula 1,

Formula 1
wherein R1, R2, R3 and R4 is selected independently from fluorine, hydrogen, methyl, fluoromethyl; and n is any number selected from 1 to 10.
comprising the steps of:
a) adding C1-10 alkanols and a radical initiator in a reactor apparatus;
b) adding a compound of formula 2,

Formula 2
in the reactor apparatus to obtain the compound of formula 1; and
c) isolating the compound of formula 1.
wherein, the reactor apparatus consists of ‘n’ number of reactors connected in a series, wherein vent of each reactor is connected to the inlet of subsequent reactor, as depicted in Figure 1.
2. The process as claimed in claim 1, wherein the radical initiator is selected from a peroxide of the following formula 3.
R5—O—O—Y—R6
Formula 3
wherein Y is carbon or a keto group. R5 is a C1—20 aliphatic hydrocarbon group, and R6 is a C1—20 aliphatic hydrocarbon group, or an aromatic hydrocarbon group.
3. The process as claimed in claim 1, wherein the isolation of compound of formula 1 is performed using distillation at a pressure in the range of 300mmHg to 40 mmHg at 55-60°C.
4. The process as claimed in claim 1, wherein the compound of formula 1 is obtained with a dimer impurity in the range of 0.1 to 2.5% and trimer impurity in the range of 0 to 1%.
5. The process as claimed in claim 1, wherein the reaction is carried out at a temperature selected in the range of 40 to 60°C.
6. The process as claimed in claim 1, wherein the compound of formula 1 has a selectivity in the range of 90 to 98%.
7. The process as claimed in claim 1, wherein the process of the present invention is either a batch process or a continuous process.
8. The process as claimed in claim 7, wherein in the batch process, the unreacted compound of formula 2 in last reactor is quenched using bromine scrubber at a temperature selected in the range of 0 to 30°C.
9. The process as claimed in claim 7, wherein in the continuous process, the unreacted compound of formula 2 is recycled back to the first reactor.

10. The process as claimed in claim 7, wherein in the continuous process, the reaction apparatus consists of n number of reactors connected in series, wherein vent of each reactor is connected to the inlet of subsequent reactor and the vent of last reactor is connected to inlet of first reactor.