|Title of Invention||
"AN IMPROVED PROCESS FOR THE PRODUCTION OF CITRONELLOL"
|Abstract||An improved process for the production of Citronellol by reducing Citronellol, citral, geraniol or mixture thereof and of essential oils containing these compounds with a novel modified Raney Nickel catalyst optionally in the presence of an organic solvent such as herein described at a temperature in the range of 30 to 100 ° C , at a pH in the range of 4 to 10 , under pressure of hydrogen in the range of 15 to lOOpsi for a period in the range of 6 to 20hrs , recovering the product by known methods.|
|Full Text||This invention relates to an improved process for the production of citronellol. More particularly this invention relates to direct reduction / hydrogenation of aldehydes ,allylic aldehydes and allylic alcohols particularly of citronellal, citral and geraniol and/or mixture of these compounds and of essential oils containing these compounds (ex. Eucalyptus citriodora, Java citronella, lemon grass, Litsea cubeba and other oils) by using modified Raney Nickel catalyst with suitable modifiers to protect other isolated unsaturated centers in the molecule in varied solvent media under optimum conditions of temperature, pressure, pH and time to get perfumery grade citronellol of high purity without or with a trace of dihydrocitronellol. Modified catalyst used for the preparation of citronellol is prepared and claimed in our copending application No. NF - 338/98.
Reduction of aldehydes and allylic aldehydes proceeded efficiently by heterogenous catalysis with modified nickel catalyst under blanket of hydrogen to give corresponding saturated alcohols in high yields. Most of the allylic alcohols are also reduced efficiently, but isolated and sterically hindered olefins resisted the reduction.
Citronellal and citral are key important terpenic aldehydes as these form starting materials for the synthesis of citronellol and many other terpenoids.
Citral, C10H,6O , M+ 152.24 is a mixture of cis and trans isomers: Citral a (geranial) bp 27118 -119° C d20 0.888 and citral b (neral) bp27 120°C ,d20 0.8869. It occurs in oil of lemon grass (~85%) and Litsea cubeba (-75%). Citronellol, geraniol and dihydrocitronellol can be obtained by hydrogenation under optimum conditions.
Citronellal ,C10H18O, M+ 154.25, bp1013 207 -208° C, d20 0.851, occurs in Java citronella oil
(-45%), Eucalyptus citriodora oil (-85%) and Backhousia citriodora oil (-80%).It is an important starting materials for the synthesis of citronellol and hydroxycitronellal.
Citronellol is a primary alcohol [3,7-dimethyl-6-octen-l-ol], C10H16O, M+156.27; bp 224°C, nD201.4558, d20 0.8590; [α]D -5°to +6°. It is found in nature in both the forms (-)-citronellol and (+)-citronellol. (-)-Citronellol obtained from natural essential oils is also known as rhodinol and is mostly found in few essential oils like geranium and rose oils. (+)-Citronellol dominates oils of Java citronella, Boronia citriodora and Eucalyptus citriodora. Citronellol is a colorless liquid with a sweet rose like odor. The odor of (-)-citronellol is more finer than (+)-citronellol. Citronellol is one of the most widely used fragrant materials, particularly for rose notes and for many floral compositions in general.
Heterogenous catalytic hydrogenation and chemical reduction of citronellal and citral in liquid phase has been attempted by several workers using nickel, cobalt, palladium, platinum and ruthenium metal catalysts [ BASF, DE-OS 2934250, 1979, (M. Horner, M.Irgang, A.Nissen, Universal oil products [US. 3275 696, 1961 (E. Goldstar), metal hydrides [J.S. Pizey, Synthetic Reagents Vol. 1 (1974) p. 106, John wiley & Sons], and many others [Neri, G. et al, J. Chem. Technol Biotechnol. (1994) 60, 838].
Industrially, citronellol is produced by the hydrogenation of citronellal /citral over different catalysts. But all these methods gives citronellol accompanied with varying amounts of dihydrocitronellol (10% to 25%) which cannot be separated by fractional distillation economically. Such large amounts of dihydrocitronellol considerably affects the roseaous odor of citronellol to coconut like odor, thus reducing its price. To accommodate the presence of dihydrocitronellol the standards for the commercial products have been modified
accordingly by Bureau of Indian Standards. However, citronellol free from dihydrocitronellol commands much higher price and is in great demand. No concrete information is available in literature for the production of citronellol free from dihydrocitronellol, hence the necessity for development of such a process.
No prior art is available in the literature concerning the present invention.
Some of the processes mentioned above are even employed on a commercial scale but suffer for want of side reactions and are accompanied with undesirable products above tolerable limits, which are difficult to separate economically. These processes are also time consuming and are quite complicated. The present invention provides a catalytic process to convert aldehydes, allylic aldehydes and allylic alcohols into saturated alcohols in high yields without side reactions, particularly the conversion of citronellal, citral and geraniol into citronellol of high purity.
Therefore, invention of a direct hydrogenation process with heterogenous catalyst for conversion of citronellal (1), citral (2) and geraniol (3) either alone or in a mixture into citronellol (4) in a single step without side reactions is advantageous. Further the corresponding esters present in the oil also get changed into citronellol, thus affording a product of high purity.
The main object of the present invention is to provide an improved process for the production of citronellol which obviates the drawbacks of the present methods as detailed above.
Another objective of the present invention is to develop direct reduction / hydrogenation of
aldehydes ,allylic aldehydes and allylic alcohols particularly of citronellal, citral and geraniol and/or mixture of these compounds and of essential oils containing these compounds (ex. Eucalyptus citriodora, Java citronella, lemon grass, Litsea cubeba and other oils) by using modified Raney Nickel catalyst with suitable modifiers to protect other isolated unsaturated centers in the molecule in varied solvent media under optimum conditions of temperature, pressure, pH and time to get perfumery grade citronellol of high purity without or with a trace of dihydrocitronellol.
Yet another objective of the invention is to use a novel catalyst in such a way which will hydrogenate the aldehydic function or the allylic aldehydes only, without affecting the isolated double bond of the molecule so as to give the maximum yield of the product. Yet still another objective is that by employing the catalyst and the conditions mentioned in the invention, the formation of undesired side product, i.e. dihydrocitronellol is totally hindered or it is formed in traces only.
In accordance with this invention we have found that in the presence of modified hydrogenation catalysts along with additives, in hydrogen atmosphere under pressure, these compounds or oil containing these compounds are converted into citronellol without any side reactions.
Nickel and cobalt are important hydrogenation catalyst because of their ability to chemisorb hydrogen. Raney Nickel is one of the most important catalysts of nickel and is used widely in laboratory and industrial hydrogenation processes. It is the most active and the least specific nickel catalyst and also has been used in continuous hydrogenation processes. The activity and specificity of nickel catalyst is also very much dependent upon its method of
preparation and other parameters of temperature, time and mode of addition. A variety of nickel catalysts are available which are used for specific purposes. The hydrogenation of unsaturated aldehydes and ketones in the presence of Raney Nickel is a complex process and mixture of 3 products viz, saturated carbonyl, unsaturated alcohols and the saturated alcohols, may well be obtained. In general, mild conditions lead to a predominance of saturated carbonyl whilst more forcing conditions favour the saturated alcohols.
Reney Nickel in general, cannot be used directly for the hydrogenation of aldehydic functions in presence of isolated olefinic centers because of its activity to hydrogenate both the centers. It is therefore, required to modify the catalyst in such a way that only the aldehydic function or allylic aldehydes or allylic alcohols are hydrogenated into saturated alcohols without affecting the isolated olefinic centers.
It is, therefore, the purpose of this invention to devise a suitable modified Raney Nickel catalyst which could hydrogenate only the aldehydic or allylic aldehydic/allylic alcoholic functions without hydrogenating the isolated double bond.
Accordingly the present invention provides an improved process for the production of citronellol which comprises reducing citronellal, citral, geranial or mixture thereof and of essential oils containing these compounds with a novel modified Raney Nickel catalyst, optionally in presence an organic solvent of such as herein described, at a temperature in the range of 30 to 100°C, at a pH in the range of 4 to 10, under pressure of hydrogen in the range of 15 to 100 psi for a period in the range of 6 to 20 hr, recovering the product by known methods.
In an embodiment of the present invention the organic solvent used may be such as alkanols,
ethyl acetate, methyl acetate, hexane, heptane, decane, dodecane, hexadecane .
The present invention describes a process for direct reduction / hydrogenation of aldehydes ,allylic aldehydes and allylic alcohols particularly of citronellal, citral and geraniol and/or mixture of these compounds and of essential oils containing these compounds (ex. Eucalyptus citriodora, Java citronella, lemon grass, Litsea cubeba and other oils) by using modified Raney Nickel catalyst with suitable modifiers to protect other isolated unsaturated centers in the molecule in varied solvent media under optimum conditions of temperature, pressure, pH and time to get perfumery grade citronellol of high purity without or with a trace of dihydrocitronellol.
We have found that the most suitable catalyst for the present inventions comprises a moderately active modified Raney nickel type catalyst at suitable temperature/and pressure applied under the conditions of hydrogenation in the presence of hydrogen above atmospheric pressure. In some cases mineral acids, inorganic & organic bases, salts of Group I, Group II and Group VIII metals are used as modifiers to retard or check the hydrogenation of isolated olefmic centers.
Nickel catalyst suitable for the present operation is prepared from nickel-aluminum alloy in the presence of modifiers like organic and inorganic bases and/or in the presence of salts of Group I, Group II & Group VIII metals and by leaching of alloy with lye at a temperature of 0°-100°C. It is, of course convenient to use hydrocarbons and alcohols as a medium and very convenient to use reaction mixture itself.
In general the usual relationship of catalyst activity, temperature, pressure, medium and time,
along with other physical and chemical parameters apply in the present case. It is important to optimize all the above mentioned conditions in order to get the desired product. The above mentioned catalyst was also employed to reduce some other aldehydes, allylic aldehydes and allylic alcohols. In every case saturated alcohols were obtained without any side reactions and isolated olefms survived the reaction conditions employed. The chemically/ catalytically treated reaction product is suitably filtered/ centrifuged and rectified in batch fractionating column separating citronellol as a technically pure high boiling fraction. The technically pure citronellol is further purified, if required, by refractionation to afford high perfumery grade citronellol.
The invention is described further with reference to examples given below. These examples should not be construed as to restrict the scope of the invention.
Sodium hydroxide (400g.) and distilled water (1500ml.) were taken in a glass beaker and contents cooled to -5° C with vigorous stirring . Nickel-Aluminum alloy (300g.) was added slowly at such a rate that the reaction temperature remained below -5° C . The reaction mixture was further stirred additionally for six hours at 10° C . The catalyst washed with water and modified by adjusting pH to 10-12 by addition of sodium carbonate, sodium bicarbonate and triethyl amine. The selectivity was further modified by addition of barium sulphate (2.5%) and ferric sulphate. The mixture of catalyst and additives was further stirred for four hours at -10° C and allowed to settle down. The catalyst was used directly for the reductions.
In a stainless steel reaction vessel fitted with a powerful mechanical agitator, a pressure gauze,
a thermometer and a hydrogen inlet valve connected to hydrogen source are placed citronellal (90% purity) (700 g) dissolved in a solvent like ethanol (10 times). Then modified nickel catalyst (50 g) modified with sodium bicarbonate -calcium sulphate (1:2) is poured in the vessel with the help of solvent and agitator is kept on. The valves are adjusted and hydrogen gas injected through the valve till the gauze records a pressure between 50 lbs/in2. The gas pressure is maintained for a period of 15 hours at a temperature between 85° C, till the time the absorption of gas ceases. The agitation is then stopped, gas released and the catalyst filtered out. The solvent is then removed under pressure to yield a product (700g) rich in citronellol . Finally, pure citronellol is obtained by fractionation under reduced pressure.
Eucalyptus citriodora oil (1.0 kg) with aldehyde content of 70 % mixed with ethyl acetate (5 kg) is placed in the reaction vessel fitted with a pressure gauze a mechanical stirrer a thermometer and hydrogen gas inlet. Modified nickel catalyst (40 g) along with sodium carbonate (10.0 g.) and barium sulphate (5.0 g.) is then added through the valve and pressure kept between 75 lbs/in2 and temperature maintained between 35°C. The hydrogen gas supply is continued till the mixture no longer records any further absorption. Then the hydrogen valves closed and the vessel degassed. The catalyst is then filtered and the solvent removed under reduced pressure to yield the oil (1.0 kg) which on GC analysis showed citronellol (74%), unreacted citronellal 0.5%, and dihydrocitronellol 1.0%
Java citronella oil (1.0 kg) is placed in the reactor and diluted with solvent methanol (7 times). The agitator is started and the mixture vigorously agitated. Modified nickel catalyst (120 g) along with iron sulphate (5.0 g.) and sodium carbonate (4.5 g.) is then poured in the
reactor through the opening. All the openings are closed and hydrogen gas pumped in through the inlet valve and pressure kept between 25 Ibs for a period of 20 hours. After the completion of the reaction, the catalyst is filtered out and the solvent removed to get the full recovery of the product which on GC analysis showed citronellol (93%) and geraniol (7%). Example -5
In the reactor fitted with all the necessary gadgets are placed lemon grass oil (1.0 kg) having a citral content of 75%. The oil is diluted with the solvent isopropanol (6 times) and the mechanical agitator started. Then nickel catalyst (150 g) modified with copper sulphate (15.0 g.) and sulphuric acid (1.0 ml) is fed through the opening and the vessel evacuated. The hydrogen inlet valve is opened and hydrogen gas injected to maintain the required conditions. After the necessary conditions have been maintained and reaction complete, the vessel is degassed and the catalyst filtered out to recover the oil. The solvent is then removed under reduced pressure to yield the reduced oil (1.0 kg) GC analysis showed that whole of citral has changed into citronellol. Advantages:
1. The main advantage of the present invention is to provide a selective process for the
transformation of substituted aldehydes, a, /3-unsaturated aldehydes and allylic alcohols
into corresponding saturated alcohols without side reactions.
2. Provide a process that does not disturb the isolated olefmic linkages in the molecules
which results in the product of high purity.
1. An improved process for the production of citronellol which comprises reducing
citronellal, citral, geranial or mixture thereof and of essential oils containing these
compounds with a novel modified Raney Nickel catalyst, optionally in presence an
organic solvent such as herein described, at a temperature in the range of 30 to
100°C, at a pH in the range of 4 to 10, under pressure of hydrogen in the range of 15
to 100 psi for a period in the range of 6 to 20 hr, recovering the product by known
2. An improved process as claimed in claim 1 wherein organic solvent used alkanols,
ethyl acetate, methyl acetate, hexane, heptane, decane, dodecane, hexadecane.
3. An improved process as claimed in claims 1 to 2, wherein the product is obtained by
filtering out the catalyst and the crude product fractionated to get a product of above
4. An improved process for the production of citronellol of the drawing accompanying
this specification substantially as herein described with reference to examples.
|Indian Patent Application Number||728/DEL/1999|
|PG Journal Number||13/2009|
|Date of Filing||14-May-1999|
|Name of Patentee||COUNCIL OF SCIENTIFIC AND INDUSTRIAL RESEARCH|
|Applicant Address||RAFI MARG, NEW DELHI-110001, INDIA.|
|PCT International Classification Number||C07C 29/14|
|PCT International Application Number||N/A|
|PCT International Filing date|