Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
2001-06-12
2002-06-11
Padmanabhan, Sreeni (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
C568S449000, C568S450000
Reexamination Certificate
active
06403839
ABSTRACT:
The present invention relates to a process for making butyraldehyde by hydrolysing an n-butenyl ester to form the corresponding n-butenyl alcohol and isomerising the latter to form butyraldehyde.
It is known that butyraldehyde can be produced by a number of routes. For instance, U.S. Pat. No. 5,705,707 discloses a method of making n-butyraldehyde and/or n-butanol by reacting butadiene with an alcohol in the presence of an acidic catalyst. The reaction produces a mixture of isomeric adducts, 1-alkoxybutene-2 (a) (also known as crotyl ether) and 3-alkoxybutene-1 (b):
CH
3
.CH═CH.CH
2
.OR (a)
CH
2
═CHCH(OR).CH
3
(b)
Compound (b) can be isomerised into compound (a). Compound (a) is isomerised in the presence of a homogeneous or heterogeneous transition metal catalyst to form the enol ether of the formula (c):
CH
3
CH
2
CH═CHOR (c)
Ether (c) reacts with water to liberate butyraldehyde. This hydrolysis reaction is catalysed by acids and bases. The butyraldehyde product can be hydrogenated with suitable homogeneous or heterogeneous catalysts to yield n-butanol. Thus compound (c) in the presence of water and hydrogen and a homogeneous or heterogeneous catalyst produces butanol and the parent alcohol ROH. The parent alcohol can then be recycled to the addition reaction stage.
A similar isomerisation hydrolysis reaction has been repeated with amines in DE-A-4431528. This document describes a process for the production of butyraldehyde which comprises the addition of an amine to a butadiene. The reaction produces a mixture of isomers, CH
3
CH═CHCH
2
NR
2
and CH
3
CH(NR
2
)CH═CH
2
. The CH
3
CH(NR
2
)CH═CH
2
isomer is recycled back to the addition reaction, whilst the CH
3
CH═CHCH
2
NR
2
isomer is converted to the corresponding enamine, CH
3
CH
2
CH═CHNR
2
. This enamine is hydrolysed to produce butyraldehyde for possible further processing and also liberates the initial amine for re-use. The butyraldehyde may be hydrogenated to the corresponding alcohol, if desired. The process of DE-A-4431528 is summarised in the diagram below:
The selectivity of the above processes has been found to be limited by the formation of by-products. Such by-products include C8 and higher species formed, for example, by dimerisation and oligomerisation reactions of C4 species. In the process of DE-A-4431528 , by-products may also be produced by amine catalysed aldol condensation reactions of butyraldehyde.
We have now found that the selectivity of the butyraldehyde production process can be increased by forming butyraldehyde from a butenyl ester.
Accordingly, the present invention provides a process for making butyraldehyde from an n-butenyl ester of a carboxylic acid, said process comprising i) hydrolysing the n-butenyl ester to form the corresponding n-butenyl alcohol and ii) isomerising the n-butenyl alcohol produced in step i) to form butyraldehyde.
By “isomerising” is meant performing any process which results in the direct or indirect conversion of the n-butenyl alcohol to butyraldehyde.
Steps i) and ii) may be carried out simultaneously or sequentially. Whilst carrying out steps i) and ii) simultaneously may allow the process to be operated more economically, the sequential hydrolysis and isomerisation stages may increase the selectivity of the overall process.
Step i) may also be carried out before step ii). Thus, in one embodiment of the present invention, n-butenyl ester is first hydrolysed to form n-butenyl alcohol, which is conveniently separable from the hydrolysis mixture as an azeotrope. The separated n-butenyl alcohol is then isomerised into the butyraldehyde product.
Preferably, the n-butenyl ester is an n-butenyl ester of a saturated, aliphatic carboxylic acid.
In the present process, the n-butenyl ester (also known as “crotyl ester”) may not be readily available commercially. Instead it may be produced by reacting butadiene with a saturated, aliphatic carboxylic acid. As butadiene is a relatively inexpensive by-product of the refining process, it provides a convenient feedstock for making butyl esters. Thus, a preferred embodiment of the present invention provides a process for the production of butyraldehyde which comprises:
a) the addition reaction of butadiene to a carboxylic acid to produce a mi)cture of sec-butenyl ester and n-butenyl ester; and
b) (i) hydrolysing the n-butenyl ester formed in step a) to form the corresponding n-butenyl alcohol, and (ii) isomerising of the n-butenyl alcohol produced in step bi) to form butyraldehyde.
Steps (i) and (ii) may be carried out simultaneously or sequentially.
The diagram below summarises the reactions which may take place in this preferred embodiment of the invention.
In step a), butadiene is reacted with a carboxylic acid R′CO
2
H in the presence of an addition catalyst, catalyst 1. Catalyst 1 may be a homogeneous or heterogeneous catalyst. Heterogeneous catalysts may be advantageous in certain situations as they facilitate separation of, for example, reaction products from the reaction mixture. They may also allow the catalyst to be conveniently separated from reaction by-products (which typically comprise high boiling point butadiene oligomeric species). The preferred catalysts are based on strong acid ion-exchange resins, such as Amberlyst 15® and Amberlite IR120®. Other suitable examples of heterogeneous catalysts include fluorinated ion-exchange resins such as Nafion®, phosphoric acid functionalised polymers, and acidic oxides, for example, HY zeolites.
A proportion of the acidic sites of such ion-exchange catalysts may be exchanged with bulky counterions, such as alkyl pyridinium, quaternary alkyl ammonium, quaternary arsonium and quaternary phosphonium. These counterions exchange with some of the acid sites on the support and can be added to the catalysts as salts, such as halides, sulphates or carboxylates.
The heterogeneous catalyst phase may be a partially or fully insoluble liquid phase. Such catalysts may take the form of acidic ionic liquids, liquid acidic polymers and partially solvated polymers. The catalyst may also be a solid phase, for example, I) an HY zeolite, II) a strong acid macroreticular, macronet or gel ion-exchange resin, or III) a heteropolyacid of tungsten or molybdenum, which has been ion-exchanged and/or supported on a carrier material.
In certain circumstances, the activity of heterogeneous catalysts may decrease considerably after prolonged periods of use. In such cases, it may be advantageous to carry out the process of the present invention in a homogeneous phase. Suitable homogeneous catalysts include sulphonic acids, heteropolyacids, triflic acid (i.e. trifluoromethane sulphonic acid) and triflate salts. Suitable heteropolyacids include Keggin structure heteropolyacids based on tungsten, and strong acid ionic liquids such as those described in prior published EP-A-693088, WO-A-95/21872 and EP-A-558187. Suitable organic sulphonic acids include methane sulphonic acid, p-toluenesulphonic acid and sulphonated calixarenes. Examples of triflate salts include lanthanide triflates, such as lanthanum trifluoromethanesulphonic acid salts.
The presence of water as a reaction adjuvant can also beneficially affect the activity and selectivity of the catalysts. It has been found that moderately low levels of water are required: at levels above 5%w/w the catalyst activity is significantly reduced, whereas at levels below 0.05%w/w, the activity though high is rapidly lost due to deactivation of the catalyst. Consequently the water level in the reaction zone is suitably in the range from 0.05 to 5%w/w on the carboxylic acid, preferably from 0.05 to 1%w/w.
The butadiene feedstock may be employed either as a purified chemical, or in the form of a hydrocarbon stream comprising butadiene. Such hydrocarbon streams include refinery streams such as mixed C4 streams containing butadiene, as well as other C4 species such as butane, 1-butene, 2-butene, isobutane, and isobutene. The addition reaction (step (a)) can be used to remove butadiene from s
BP Chemicals Limited
Nixon & Vanderhye
Padmanabhan Sreeni
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