Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Reexamination Certificate
1999-03-10
2001-01-30
Shippen, Michael L. (Department: 1621)
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
Reexamination Certificate
active
06180839
ABSTRACT:
The present invention relates to a continuous process for the preparation of dimethylvinylcarbinol by isomerizing prenol in aqueous solution in the presence of protic acids.
Dimethylvinylcarbinol (DMVC; 2-methyl-3-buten-2-ol) is an important intermediate in industrial organic chemistry and serves in particular as an intermediate for the preparation of fragrances or else as an additive in soaps and detergents.
It is known that 3-methyl-2-buten-1-ol (prenol) can isomerize under acid catalysis to DMVC. This isomerization corresponds to a 1,3 migration of the hydroxyl group and a corresponding shift of the double bond, as is shown in the equation below:
This migration of a double bond and of a substituent is known for allyl compounds and is generally referred to as allyl rearrangement. Allyl rearrangements of allyl alcohols are equilibrium reactions.
A general overview of the isomerization of allyl alcohols, catalyzed by protic acids, can be found, for example, in Houben-Weyl: “Methoden der organischen Chemie” [Methods in Organic Chemistry], volume VI, 1b, page 528 et seq., Stuttgart, 1984. This describes, inter alia, that such isomerizations can be carried out in a particularly simple manner, the corresponding primary alcohol having an internal C═C double bond being formed from a tertiary allyl alcohol having a terminal C═C double bond.
In keeping with this knowledge, in the past, the isomerization of DMVC, a tertiary allyl alcohol, has in particular been used industrially to give its isomer, prenol, a primary allyl alcohol. Both compounds have, for example, been used in the fragrance industry as base substance for the preparation of alcohols of the terpene series. Based on the earlier widespread industrial carbide-acetylene chemistry, dialkylalkenylcarbinols, such as DMVC, were readily accessible by base-induced condensation of 1-alkynes, such as acetylene, with ketones, such as acetone, and subsequent hydrogenation of the triple bond to a double bond. Nowadays, acetylene is a comparatively rare and expensive raw material. On the basis of petrochemical raw materials which is common nowadays, olefins such as dialkylalkenes, such as isobutene, are by contrast readily accessible. These can be processed by condensation with aldehydes, such as formaldehyde, and subsequent isomerization of the double bond readily to give prenol or prenol derivatives, such as prenol substituted by organic radicals. In industry, there is thus nowadays a particular need for a process which can be used to prepare the tertiary allyl alcohol DMVC from the primary allyl alcohol prenol.
SU-A 181 090 describes a process for the preparation of DMVC by dehydration of 3-methyl-1,3-butanediol, in which a mineral acid, in particular sulfuric acid, in a concentration below 1% by weight (corresponding to a pH above 0.7), preferably in a concentration of from 0.3 to 0.5% by weight, is used as catalyst. This preferred concentration range corresponds to a pH range from 1.0 to 1.2. This publication also teaches that it is also possible to use the isomeric alcohols C
5
H
9
OH (3-methyl-3-buten-1-ol and prenol) as starting materials in this process. Furthermore, the example given shows that when the disclosed process is carried out, high amounts of by-products are produced, which must be regularly removed discontinuously from the reactor. The yield of DMVC from 3-methyl-1,3-butanediol is only 70%. Yield data for the process variant mentioned starting from prenol are not given. Similarly, there is no information regarding the relationship between acid concentration, reaction volume and input flow rate of fresh prenol.
According to J. Gen. Chem. USSR, 21 (1951) pages 1235-1241, A. I. Lebedeva and L. L. Schukovskaya investigated the dependency of the isomerization of DMVC on the pH of the reaction medium and on the reaction temperature used for a reaction time of 30 hours. They found that isomerization of the DMVC used took place at room temperature only at a pH of 1.29 or below. At a pH of 1.32 or above, no isomerization of the DMVC was observed either at room temperature or in a boiling water bath. The discontinuous process has a complicated workup which cannot be utilized economically on an industrial scale.
In Bull. Acad. Sci. USSR, Chem. Ser. 1946, 419-426, I. N. Nazarov, I. N. Azerbaev and V. N. Rakcheeva teach that the isomerization of dialkylvinylcarbinols, i.e. the tertiary allyl alcohols, into the corresponding primary allyl alcohols proceeds “quite smoothly” in a temperature range from 60 to 100° C. under the influence of 0.1% strength by weight sulfuric acid, i.e. at a pH of about 1.7, while at room temperature the isomerization is carried out under the influence of 1-5% strength sulfuric acid, i.e. at a pH of about 0.7 and below. This publication also teaches that in the case of a sulfuric acid concentration of 0.01%, i.e. a pH of 2.7, the isomerization process itself proceeds too slowly at a temperature of 100° C. Thus, all of the known examples for the isomerization of allyl alcohols were carried out with high acid concentrations, i.e. a low pH of no more than 1.5 or even significantly below 1. The described process is unsuitable for the economic preparation of DMVC.
JP-A-54/061110 describes a process for the isomerization of allyl alcohols using large amounts of boric acid as catalyst. From 0.1 to 60% by weight, in particular from 1 to 30% by weight, of boric acid are used. Conversions above 90% are only achieved with boric acid concentrations above 7% by weight of boric acid; at even higher amounts of boric acid the selectivity of the isomerization drops rapidly. The achieved yields are below 85%. No information is given regarding the type of column used and the reflux ratio used. The examples show that the DMVC obtained was contaminated with prenol. The described workup is very complicated. It is not possible to use the described process to prepare DMVC from prenol economically.
A disadvantage of all of the known processes for the isomerization of allyl alcohols was that they produce relatively large amounts of undesired by-products.
There continued to be, therefore, a great need for a process which enables a continuous preparation of pure DMVC from prenol in a simple, inexpensive and very selective manner but with high space-time yields.
Accordingly, the invention provides a process for the continuous preparation of dimethylvinylcarbinol (DMVC) by continuously reacting prenol with the aqueous solution of a protic acid in the still or in the lower part of a rectification column while distilling off the DMVC formed in the form of an azeotropic mixture with water, which comprises
a) during the reaction ensuring that as far as possible no liquid two-phase mixture forms in the reaction mixture,
b) distilling off the DMVC which forms at a reflux ratio of at least 2 and
c) setting the reaction volume and/or the amount of prenol added per hour and/or the concentration of protons in the reaction mixture in such a manner that the quotient, defined as residence time concentration coefficient, of the reaction volume and the volume of prenol added per hour multiplied by the concentration of protons in the reaction mixture has a value between 0.001 h·mol/l and 1 h·mol/l, preferably from 0.01 to 0.15 h·mol/l.
Only when it is ensured that as far as possible no liquid two-phase mixture forms in the reaction mixture is the formation of by-products largely suppressed.
In order to prevent the formation of a liquid two-phase mixture in the reaction mixture, in addition to using quantities of prenol which are not too large, it is important to continuously take from the reaction mixture in the reaction volume a partial stream, pass the latter over a phase separation vessel, completely or at least largely remove there the small quantities of organic substances formed which are insoluble or only partially soluble in water, and then return the aqueous phase to the reaction volume.
An important factor for the desired high DMVC yield is the presence of a sufficiently high heating capacity to distil off the DMVC w
Aquila Werner
Kiefer Matthias
Pahl Melanie
Sch{umlaut over (a)}fer-L{umlaut over (u)}derssen Ulrich
Siegel Wolfgang
BASF - Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Shippen Michael L.
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