Organic compounds -- part of the class 532-570 series – Organic compounds – Oxygen containing
Patent
1997-01-06
1999-05-25
Barts, Samuel
Organic compounds -- part of the class 532-570 series
Organic compounds
Oxygen containing
568843, C07C 3342
Patent
active
059070706
DESCRIPTION:
BRIEF SUMMARY
This invention relates to halogenated alcohols and more particularly to a process of preparing halogenated alcohols from haloalkanes.
The preparation of halogenated alcohols such as 1,1,1-trichloro-4-methyl-3-penten-2-ol has previously been described (in for example J. Chem.Soc. (C), 1976,670). In this process a Grignard reagent such as isobutenylmagnesium chloride is reacted with chloral. However the Grignard reaction is essentially a laboratory procedure and is not inherently suitable for industrial production. An alternative known process involves the reaction of chloral with isobutylene under the conditions of the Prins reaction but this can lead to a mixture of the desired product with the isomeric 1,1,1-trichloro-4-methyl-4-pentene-2-ol and further treatment to isomerise this is required.
The present invention is concerned with an improved process which is applicable to the preparation of the desired compounds and which is suitable for industrial manufacture.
Accordingly the present invention provides a process for preparing a halogenated alcohol of formula: fluoro, although not all of X.sup.1, X.sup.2 and X.sup.3 are necessarily the same, which comprises reacting a compound of formula:
Compounds of formula (I) which may be made by the process include those wherein X.sup.1, X.sup.2 and X.sup.3 are all chloro or all bromo. Particular examples of such compounds of formula (I) include 4-hydroxy-2-methyl-5,5,5-tribromopent-2-ene, and 4-hydroxy-2-methyl-5,5,5-trichloropent-2-ene.
The compounds of formula (II) which are useful in the process of the invention are halomethanes containing a single hydrogen atom, such as chloroform, and bromoform. 3-Methylbut-2-en-1-al is also known as senecialdehyde.
The process is conducted in the presence of a strong base, which is believed to act by generating a perhaloalkyl ion which then reacts with the aldehyde. Suitable strong bases include alkali metal lower alkoxides, such as sodium or potassium alkoxides containing up to 6 carbon atoms, for example sodium isopropoxide, potasium isopropoxide, sodium t-butoxide and potassium t-butoxide, but other bases such as alkali metal hydrides, for example sodium hydride, and amides, for example sodamide, may also be used.
The process is preferably conducted at low temperatures to avoid the production of unwanted by-products. A preferred temperature is within the range -80.degree. C. to 0.degree. C., especially where a polar aprotic solvent is used. Particular examples of polar aprotic solvents which may be useful in the process include amides such as dimethylformamide, dimethylacetamide, dibutylacetamide, cyclic ethers such as tetrahydrofuran, tetrahydropyran and dioxan, glycol ethers such as ethylene glycol dimethyl ether, and ethylene glycol diethyl ether, and sulphoxides such as dimethyl sulphoxide. However other inert solvents such as aromatic hydrocarbons e.g. toluene may also be used.
The process is useful to produce the compounds of formula (I) in good yield and purity and allows for easy isolation of the desired product. Any unreacted or excess compound of formula (II) can be readily recovered and recycled.
The compounds of formula (I) are useful as intermediates in a variety of synthetic procedures for the manufacture of useful products. Thus 4-hydroxy-2-methyl-5,5,5-trichloropent-2-ene may be used in the manufacture of permethrin acid, a key intermediate for pyrethroid insecticides, by the process set out in UK Patent No. 1528944.
The process of the invention is illustrated by the following Examples.
EXAMPLE 1
This Example illustrates the preparation of 4-hydroxy-methyl-5,5,5-tribromopent-2-ene.
Sodium t-butoxide (1.2 ml of a 42% solution in dry dimethylformamide) was added dropwise over a period of 20 minutes to a stirred mixture of bromoform (1.14 g), 3-methylbut-2-ene-1-al (0.32 g) and dry tetrahydrofuran (15 ml) maintained at a temperature of -65.degree. C. by external cooling under a nitrogen atmosphere, and the stirred mixture maintained at that temperature for a further 30 minutes after completion of the addi
REFERENCES:
Merz and Tomahogh, Chem. Ber, 110, 96-106 (1977), "Reactions of Aldehydes and Ketones with the Makosza Dichlorocarbene Reagent".
Kaspar and Wiechert, Chemische Berichte Jahrg, 91, 2664-2670 (1958), "Uber die Einwirkung von Haloform auf Steroidcarbonylfunktionen".
Shono et al., Additttion of Trichloromethyl Anion to Aldehydes or Vinyl Acetate, Tetrahedron Lett. 1981, 22(9), 871-4, 1981.
Shono et al., Chain Reactions Induced by Cathodic Reactions, J. Org. Chem., 50, 2527-2533, 1985.
Bowden Martin Charles
Brown Stephen Martin
Perrior Trevor Robert
Barts Samuel
Zeneca Limited
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