JPH1160541A - Production of dialkyl carbonate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject carbonate useful as a raw material for diphenyl carbonate in a high space-time yield by reacting urea with an alcohol in the presence of a catalyst in a high boiling point solvent by the use of a continuous multi-stage reactor to compact the size of the reactor, reduce the initial charge amount of the low boiling point alcohol, maintain a high reaction temperature and reduce the total amount of the reaction solution. SOLUTION: This method for producing a dialkyl carbonate comprises feeding (A) an alcohol in an amount of <=2-fold moles the fed amount of the component B, (B) urea, (C) a catalyst and (D) a high boiling point solvent having a boiling point of >=180 deg.C in an amount of 0.1-10 fold moles the fed amount of the component B at an arbitrary stage of a continuous multi-stage reactor, continuously taking out the by-produced ammonia frog each stage in a gaseous state, simultaneously continuously taking out the reaction solution containing the dialkyl carbonate from each stage, further feeding the upper stage reaction solutions into the lower stage reaction solutions, and taking out the reaction solution containing the dialkyl carbonate from the final stage.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a dialkyl carbonate. More specifically, the present invention relates to a method for producing a dialkyl carbonate by reacting urea or an alkyl carbamate with an alcohol in the presence of a catalyst. Dialkyl carbonate is a compound useful as a raw material for diaryl carbonate, especially diphenyl carbonate.

[0002]

2. Description of the Related Art A method for producing a dialkyl carbonate by reacting urea and an alcohol is disclosed in JP-A-55-102.
No. 542, JP-A-55-102543 and JP-A-57-26645 disclose a method for producing a dialkyl carbonate by reacting an alkyl carbamate with an alcohol.
There is a description in the issue. The catalyst for this reaction is described in JP-A-57-175147.

[0003] The conventionally known method for producing a dialkyl carbonate by reacting urea or an alkyl carbamate with an alcohol requires a high reaction temperature of 180 ° C or more and a reaction time of 8 hours or more. . Further, dialkyl carbonates which can be produced at normal pressure by this method have been limited to the case where a high-boiling alcohol such as octanol is used as a raw material. That is, when synthesizing a dialkyl carbonate from an alcohol having a boiling point of 180 ° C. or less and an alkyl carbamate, it is necessary to allow the reaction to proceed for an extremely long time or to increase the pressure in order to obtain a sufficient reaction temperature.

Japanese Patent Application Laid-Open No. 57-26645 discloses an example in which dibutyl carbonate is produced from butyl carbamate and butanol as raw materials. According to this method,
The reaction is carried out under pressurized conditions of 9 to 10 bar, but the conversion of carbamate after 7 hours is only 40%.
Furthermore, when isobutanol is used, it takes 40 hours to complete the reaction, and a practical reaction rate has not been obtained. Further, when the reaction is carried out under pressure, the generated ammonia must be removed while maintaining the pressure, so that the apparatus becomes complicated and expensive.

[0005] The present inventors have proposed a method for solving this problem.
Japanese Patent Application Nos. 9-63147 and 9-85251 have already disclosed methods for performing a reaction in the presence of a high boiling point solvent. By using this method, even when using a low-boiling alcohol, at a pressure near normal pressure,
It became possible to obtain dialkyl carbonate at a practical reaction rate. However, the use of a solvent causes a problem that the size of the reaction apparatus becomes large.

[0006]

SUMMARY OF THE INVENTION In view of the above problems, the present invention aims at reducing the size of a reaction apparatus and increasing the reaction rate at a pressure near normal pressure even when using a low-boiling alcohol. It is an object of the present invention to provide a method for producing a dialkyl carbonate which can be maintained and obtain a high space-time yield.

[0007]

Means for Solving the Problems The present inventors have attempted to reduce the size of individual reactors by making the reaction continuous, and to reduce the initial charge of a low-boiling alcohol which causes a reduction in the reaction temperature. By using a method in which insufficient alcohol is added as needed as the reaction progresses, it becomes possible to reduce the amount of the high-boiling solvent used, and to maintain the high reaction temperature (that is, high reaction rate) while maintaining the total reaction solution volume. Has been found to be possible.

That is, the present invention provides a method for producing a dialkyl carbonate by reacting urea with an alcohol in the presence of a catalyst and a high-boiling solvent having a boiling point of 180 ° C. or higher. , And ammonia continuously produced in the reaction in each stage is continuously extracted in gaseous form from each stage, and the reaction solution containing dialkyl carbonate is continuously extracted from each stage. And producing a dialkyl carbonate-containing reaction liquid from the lowermost stage. Preferably, urea, a catalyst, and a high-boiling solvent are all introduced in the first stage, and alcohol is introduced in an optional stage depending on the reaction state.

Further, the present invention provides a method for separating a dialkyl carbonate from a reaction solution obtained from a lowermost reactor,
This is a method for producing a dialkyl carbonate using a catalyst and a high boiling point solvent in a circulating manner, and using unreacted alcohol and an intermediate carbamate as a part of a raw material.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the method for producing a diaryl carbonate of the present invention will be described more specifically.

In the present invention, the alcohol is not particularly limited as long as it is an aliphatic alcohol.
-8 aliphatic alcohols are used. Examples of these alcohols include methanol, ethanol, propanol, butanol, pentanol, cyclopentanol, hexanol, cyclohexanol, heptanol, octanol and the like (each example includes each isomer). Among these alcohols,
It is particularly preferable to use an alcohol having 3 to 6 carbon atoms because the effect of improving the reaction rate is remarkable. When the number of carbon atoms is 9 or more, the effect of adding a solvent is small because the boiling point of the alcohol is sufficiently high.

In the present invention, the alkyl carbamate is an alkyl carbamate obtained by reacting urea with the above alcohol, and is an intermediate product of the production method of the present invention. In the present invention, since the reaction of urea to alkyl carbamate and the reaction of alkyl carbamate to dialkyl carbonate occur continuously in the same reactor, there is no particular need to take out the intermediate. Conversely, the use of an alkyl carbamate as a raw material does not matter at all. Therefore, in the present invention, the alkyl carbamate recovered in the separation step can be reused as a raw material.

The high boiling solvent used in the present invention has a boiling point of 18
Solvents at 0 ° C. or higher are preferred. A solvent having a boiling point of 195 ° C. or higher is more preferable, and a boiling point of 220 ° C. or higher is more preferable, because the effect of increasing the boiling point is high. The type of the high boiling point solvent is not particularly limited, but a low polarity solvent is preferable because the solubility of ammonia is small and the discharge of ammonia to the outside of the system is assisted.

Preferred high boiling solvent species include hydrocarbons and ethers. The hydrocarbon may be an aliphatic unsaturated hydrocarbon, but a more stable saturated hydrocarbon or aromatic hydrocarbon is preferred. As the ether, any of an aromatic ether, an aliphatic ether, and an aromatic aliphatic ether can be used.

[0015] Examples of preferred hydrocarbon solvents include the following. Undecane, dodecane, tridecane, tetradecane, pentadecane, hexadecane, heptadecane, octadecane, nonadecane, eicosane, tetramethylpentadecane, dicyclohexyl; hexylbenzene, cyclohexylbenzene, heptylbenzene, octylbenzene, nonylbenzene, decylbenzene, undecylbenzene, diisopropylbenzene , Triisopropylbenzene, pentamethylbenzene, methylnaphthalene, diphenylmethane, ethylbiphenyl,
Bibenzyl (each example also includes each isomer).

Preferred examples of the ether solvent include the following. Dihexyl ether, dioctyl ether, cyclododecyl methyl ether, diethylene glycol dimethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether; butyl phenyl ether, benzyl phenyl ether, dibenzyl ether, diphenyl ether, ditolyl ether Each isomer is also included).

Known catalysts can be used. As catalysts for this reaction, many catalysts have already been described in JP-A-55-102542, JP-A-55-102543, JP-A-57-26645, JP-A-57-175147 and the like. Can also be used in the present invention. Among them, zinc, lead, copper, tin, titanium,
Of one or more metals selected from gallium and indium,
Oxides, hydroxides, halides, inorganic salts, organic acid salts,
Alkoxides, alkyl oxides and alkyl alkoxides are preferably used. Specific examples include zinc oxide, lead acetate, copper acetate, dibutyltin oxide, dioctyltin oxide, dibutyldibutoxytin, tetrabutoxytitanium, and gallium tributoxide.

The reaction is preferably carried out at atmospheric pressure,
It may be carried out in a state of reduced pressure or slight pressure of about 0.001 to 0.5 MPa in absolute pressure. If the reaction is carried out at a pressure other than the atmospheric pressure, it is necessary to discharge ammonia generated during the reaction to the outside of the system, so that the apparatus becomes somewhat complicated, for example, a pressure regulator is required in front of the reflux condenser.

In order to facilitate the discharge of the formed ammonia, the reaction is preferably carried out in a state where the reaction solution is refluxed. That is, the preferred reaction temperature is the boiling point of the reaction solution. As the reaction proceeds, the boiling point of the reaction solution increases due to consumption of alcohol. At first, an appropriate amount of alcohol may be charged and the reaction may be performed depending on the reaction temperature, or the reaction may be continued by adding an appropriate amount of alcohol and maintaining the boiling point of the reaction solution at an appropriate temperature. The reaction temperature is suitably about 140 to 260 ° C., preferably 160 to 260 ° C.
~ 240 ° C. The residence time of the reaction is suitably from 1 to 20 hours, and usually from 3 to 10 hours. Since the intermediate alkyl carbamate can be recovered and used as a raw material, it is not always necessary to complete the reaction.

The amount of the alcohol to be added is suitably 1 to 3 moles per 1 mole of urea as the sum of the amounts added to each reactor. When the raw material contains an alkyl carbamate, it is preferable to further add 0.5 to 1.5 mol of alcohol to 1 mol of carbamate. Although the entire amount of alcohol may be introduced into the first reactor, alcohol has the lowest boiling point among the reactants. Therefore, if a large amount of alcohol is added from the beginning, the boiling point of the entire reaction solution decreases. That is, the reaction temperature decreases and the reaction rate decreases. Therefore, it is more efficient to add alcohol to each reaction tank according to the progress of the reaction.

The amount of the high boiling solvent is suitably about 0.1 to 10 mol per 1 mol of urea. When the alkyl carbamate is contained in the raw material, the molar ratio is appropriately 0.1 to 10 times the sum of the moles of urea and alkyl carbamate. When an alcohol having a low boiling point is used, a higher molar fraction of the solvent is preferred because the boiling point of the reaction solution is higher (that is, the reaction temperature is higher), but the size of the reactor increases as the solvent increases. Therefore, the optimal amount varies depending on the type of alcohol and the concentration of alcohol.

The amount of the catalyst varies depending on the catalyst used.
Usually, about 0.001 to 0.5 mol is appropriate for 1 mol of urea.

The present invention is a method for continuously producing dialkyl carbonate. The production of dialkyl carbonate can be carried out by a batch reaction, more preferably a semi-batch reaction in which an alcohol is added according to the degree of the reaction, but it requires an extremely large reactor and is not practical. In the case of using a multi-stage reactor, it is possible to avoid the mixing of the reaction solution having an increased conversion rate and the unreacted raw material, and therefore it is possible to efficiently produce dialkyl carbonate by combining a relatively small reactor. .

The reaction of the present invention is carried out at or near the boiling point of the reaction solution. However, since the boiling point of the alcohol used in the present invention is lower than the required reaction temperature, a sufficient reaction rate cannot be obtained if used as it is. . Therefore, a high boiling point solvent is used in the present invention. The high boiling point solvent has the effect of raising the reaction temperature and lowering the polarity of the reaction solution to make it easier for ammonia to escape from the reaction solution.

In the continuous method, this is achieved by performing a multi-stage reaction in which tank reactors are connected, and adding alcohol to each tank as appropriate. Specifically, the liquid temperature of each reaction tank is set in advance, and when the liquid temperature rises as the reaction proceeds and exceeds a predetermined temperature, alcohol may be added so that the liquid temperature becomes the predetermined temperature. This operation can be performed automatically by combining a temperature detector and a pump. It is effective to supply a fixed amount of alcohol to each tank without adjusting the temperature more simply.

The reaction solution is continuously withdrawn from the lowermost reactor, and a separation operation is performed. As the separation method, distillation is usually used. The reaction solution contains a starting material alcohol, an intermediate alkyl carbonate, a high boiling point solvent, and a catalyst in addition to the product dialkyl carbonate, but the liquid after separating the dialkyl carbonate is circulated to the reaction system. . That is, the solvent and catalyst are reused, and the alcohol and alkyl carbamate are used as raw materials.

As the reactor used in the present invention, any continuous multi-stage reactor can be used, but a tank-type or tower-type reactor is generally used, and the number of reactor stages is 2 or more. Is required, and the number of reactor stages is preferably 3 or more.
When a tank-type reactor is used, it is necessary to attach a reflux condenser or a distillation column above the reactor to separate alcohol and ammonia.

Next, FIG. 1 shows an example of a continuous dialkyl carbonate reactor used in the continuous multistage reactor of the present invention, and the production of dialkyl carbonate from alcohol and urea will be described.

In FIG. 1, three reactors are installed in series. In the figure, 1, 2 and 3 are stirred tank reactors,
4, 5, and 6 are reflux condensers. Urea, high boiling point solvent and catalyst are continuously introduced through conduit 7 and alcohol is introduced through conduit 8
It is introduced into the reactor 1 as needed. In each reactor,
The reaction is allowed to react while refluxing. A mixed vapor of ammonia and alcohol is generated from each reactor. The alcohol is returned to the reactor by the reflux condenser 4, and the ammonia passes through the reflux condenser and is discharged from the conduit 14. The reaction liquid in the reactor 1 is continuously supplied to the reactor 2 via the conduit 11. The supply method may be an overflow type or a liquid sent by a pump. In the case of the overflow type, it is necessary to take measures such as inserting an introduction pipe below the liquid level so that the vapor generated in the reactor 2 does not return to the reactor 1. It is.
In this drawing, the pipe is partly bent and liquid sealed. The reaction is also carried out in the reactor 2 while the reaction solution is refluxed. At this time, if necessary, additional alcohol is supplied from the conduit 9. The reaction liquid in the reactor 2 is continuously supplied to the reactor 3 via the conduit 12. The reaction is also carried out in the reactor 3 while refluxing the reaction solution. At this time, if necessary, additional alcohol is supplied from the conduit 10. The reaction solution in the reactor 3 is continuously withdrawn via a conduit 13 and sent to a separation step.

As the high boiling point solvent and the catalyst introduced from the conduit 7, a liquid obtained by separating the alkyl carbonate in the separation step can be used, and it may contain the alkyl carbamate recovered in the separation step. Further, it is not always necessary to return all of these liquids to the first reactor, and a part of these liquids may be supplied to the second reactor and thereafter.

The reaction vessel does not necessarily need to be equipped with a stirrer, but may be of a type that is stirred by external circulation or the like. The volume of each reactor also need not be constant. The reflux condenser can be replaced with a distillation column. A method of treating the generated steam with one reflux cooler, for example, a method of condensing all the generated steam of the reactor 2 and the reactor 3 with the reflux cooler 4 and returning it to the reactor 1, is also possible. Is not preferable because the alcohol concentration is not maintained. However, it is preferable to have a device capable of appropriately distributing the collected vapor to each reactor.

In the present reaction, a small amount of by-products such as ammonium cyanate and ammonium carbonate is produced in a trace amount, and the pipes may be clogged during a long operation. The dissociation temperature of these compounds is about 6 at normal pressure.
Since the temperature is 0 ° C., it is preferable to keep the temperature of the pipe having a possibility of adhesion at a temperature higher than the dissociation temperature. Further, the reflux condenser is preferably operated at a temperature not lower than the dissociation pressure of these salts (not lower than 60 ° C. at normal pressure) and not higher than the boiling point of the alcohol used.

As the column type reactor, a usual multistage distillation column can be used as it is. The type of distillation column is not particularly limited, but a plate column type distillation column is preferable because a residence time is required. Specifically, a tray column using a bubble bubble tray, a perforated plate tray, a valve tray, or the like is suitable. When a tower-type reactor is used, urea, alcohol, a solvent, and a catalyst are continuously supplied to the upper part or the center part of the tray column, and ammonia is continuously extracted in gaseous form from the upper part of the distillation column. The reaction can be performed by continuously extracting the reaction solution from the lower part. Further, in this case, the mixture of urea, the solvent and the catalyst is continuously supplied to the upper or middle portion of the tray column, and the alcohol is supplied from the supply stage of the mixture and any of a plurality of lower stages. Is preferred.

FIG. 2 shows an example of a continuous reactor for dialkyl carbonate using a tower type multistage reactor, and the production of dialkyl carbonate from alcohol and urea will be described.

In the figure, 21 is a multi-stage distillation column. A mixture of urea, a catalyst and a high-boiling solvent is introduced through an inlet tube 24, and alcohol is introduced through inlet tubes 25 and 26. Ammonia generated in each stage of the multi-stage distillation column 21 reaches the top of the column, becomes a mixed vapor with alcohol, and reaches the reflux condenser 22. The vapor is cooled in the reflux condenser 22 and the alcohol is condensed, but the ammonia passes through the reflux condenser and is discharged from the conduit 27. Part of the condensed alcohol is returned to the top of the column, and the rest is introduced via conduits 28 into inlets 25 and 2
6 In each stage, the reaction liquid is continuously supplied from the upper stage, and at the same time, a part is extracted and continuously supplied to the lower stage. A part of the reaction solution reaching the lowermost stage is heated by the reboiler 23 and returned to the distillation column, and at the same time, a part is continuously withdrawn through the conduit 29 and sent to the separation step.

[0036]

EXAMPLES The present invention will be described below with reference to examples, but the present invention is not limited to these examples.

Example 1 An experiment was conducted using a three-stage continuous reactor similar to that shown in FIG. Reactors 1, 2 and 3 used the same stirring tank with a volume of 1 L, baffles and a stirrer. The alcohol used was n-butanol, the solvent was diphenyl ether, and the catalyst was dibutyltin oxide. A liquid in which urea, a catalyst and a solvent were uniformly dispersed in a premixing tank was continuously introduced into the reactor 1 through a conduit 7. Alcohol was automatically introduced through conduits 8, 9, and 10 so that the reaction temperature in each reactor was maintained at a predetermined temperature. The temperature of each reactor was set at 190 ° C. for the reactor 1, 200 ° C. for the reactor 2 and 210 ° C. for the reactor 3. Heating was performed in an oil bath attached to each reactor. Hot water at 80 ° C. was passed through the reflux condensers 4, 5, and 6. Each reactor was provided with overflow tubes 11, 12, and 13 to keep the liquid volume constant. Also, a part of the overflow pipe was bent to form a liquid-sealed portion, so that vapor generated from the reaction solution was prevented from going to an adjacent reactor. Ammonia generated from each reactor was separated from butanol by reflux condensers 4, 5, and 6, and then discharged from conduit 14. As a result of continuous reaction for 100 hours, 32.6 kg of a reaction solution was obtained from the conduit 13, and 3850 g of dibutyl carbonate was obtained by distilling the reaction solution. The total feed amount of each reactor and the yield based on urea in each reactor are shown below.

Total feed amount (100 hours) {Reactor 1 Reactor 2 Reactor 3}尿素 Urea 2336 g n-butanol 4716 g 402 g 322 g Diphenyl ether 26342 g Dibutyltin oxide 359 g

Urea based yield in each reactor {Reactor 1 Reactor 2 Reactor 3} ────────────────────────── Butyl carbamate 61.8% 34.7% 18.0% Dibutyl carbonate 15.7% 44.2% 63.8%

Example 2 The distillate of Example 1 was subjected to distillation separation of the distillate, and the forerunner and the bottom were mixed to obtain a recovered liquid. When this solution was analyzed, it was composed of the following components.

Composition per kg of recovered liquid ──────────────────────── n-butanol 30.3 g (0.409 mol) butyl carbamate 27.4 g (0.234 mol) Dibutyl carbonate 16.7 g (0.096 mol) Diphenyl ether 912.8 g (5.363 mol) Dibutyltin oxide 12.6 g (0.051 mol)

Using the same reactor as in Example 1, 290.1 g / h of this recovered solution and urea at 23.00 g / h from the conduit 7 were used.
36 g was added, and n-butanol was automatically added from conduits 8, 9, and 10 so as to reach the set temperature (the same as in Example 1). As a result of performing a continuous reaction for 100 hours in the same manner as in Example 1, 34.9 kg of a reaction solution was obtained from the conduit 13, and by distilling the reaction solution, 5070 g of dibutyl carbonate was obtained. The total feed amount of each reactor and the yield based on urea in each reactor are shown below.

Total feed amount (100 hours) {Reactor 1 Reactor 2 Reactor 3} ─────────────────────── Urea 2336 g n-butanol 5150 g 470 g 354 g butyl carbamate 796 g dibutyl carbonate 486 g diphenyl ether 26482 g dibutyl tin oxide 366 g

Urea based yield in each reactor {Reactor 1 Reactor 2 Reactor 3} ──────────────────────── Dibutyl carbonate 30.7% 63.8% 86.0%

[0045]

According to the method of the present invention, dialkyl carbonate can be obtained with a high space-time yield, and its industrial effect is great.

[Brief description of the drawings]

FIG. 1 is a flow sheet diagram of a tank-type continuous reactor of the present invention.

FIG. 2 is a flow sheet diagram of the continuous column reactor of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stirred tank type reactor 2 Stirred tank type reactor 3 Stirred tank type reactor 4 Reflux cooler 5 Reflux cooler 6 Reflux cooler 7 Mixture introduction pipe of urea, catalyst and solvent 8 Alcohol introduction pipe 9 Alcohol introduction pipe 10 Alcohol Inlet tube 11 Reaction liquid withdrawal tube 12 Reaction liquid withdrawal tube 13 Reaction liquid withdrawal tube 14 Ammonia withdrawal tube 21 Multistage distillation tower 22 Reflux cooler 23 Reboiler 24 Introductory tube 25 Introductory tube 26 Introductory tube 27 Discharge tube 28 Withdrawal tube 29 Withdrawal tube

Claims (10)

[Claims] 1. A catalyst and a boiling point of urea and alcohol of 180
In a method for producing a dialkyl carbonate by reacting in the presence of a high boiling point solvent of at least ℃, alcohol, urea,
The catalyst and the high boiling point solvent are supplied to any stage of the continuous multi-stage reactor, and ammonia produced by the reaction in each stage is continuously extracted in gaseous form from each stage, and the reaction liquid containing dialkyl carbonate is continuously extracted from each stage. And feeding the upper reaction solution to the lower reactor, and extracting the reaction solution containing the dialkyl carbonate from the lowermost stage. 2. The total amount of urea, catalyst and high boiling point solvent is first
The method for producing a dialkyl carbonate according to claim 1, wherein the alcohol is introduced into a stage, and the alcohol is supplied to an arbitrary stage depending on the reaction state. 3. A dialkyl carbonate is separated from a reaction solution obtained from a lowermost reactor, and an unreacted alcohol, a catalyst, a high-boiling solvent and an intermediate carbamate are returned to an arbitrary stage of a continuous multistage reactor. 2. The method for producing a dialkyl carbonate according to claim 1, wherein the catalyst, the high boiling point solvent and the unreacted alcohol and the intermediate carbamate are used as a part of the raw material. 4. After dialkyl carbonate is separated from the reaction solution obtained from the lowermost reactor, unreacted alcohol, catalyst, high boiling point solvent and intermediate carbamate are returned to the first stage of the continuous multistage reactor. 3. The method for producing a dialkyl carbonate according to claim 2, wherein the catalyst, the high boiling point solvent and the unreacted alcohol and the intermediate carbamate are used as a part of the raw material. 5. The method for producing a dialkyl carbonate according to claim 1, wherein the number of continuous multistage reactors is three or more. 6. The amount of the high-boiling solvent introduced is 0.1 to 10 times the mol of the urea introduced.
5. The method for producing a dialkyl carbonate according to 4. 7. The process for producing a dialkyl carbonate according to claim 1, wherein the amount of alcohol introduced in the first stage of the continuous multistage reactor is not more than twice the amount of urea introduced. 8. The method for producing a dialkyl carbonate according to claim 1, wherein the high boiling point solvent is a hydrocarbon or an ether. 9. The method for producing a dialkyl carbonate according to claim 8, wherein the high boiling point solvent is diphenyl ether. 10. The method for producing a dialkyl carbonate according to claim 1, wherein the alcohol is an aliphatic alcohol having 3 to 6 carbon atoms.