PROCESS FOR HYDROXYMETHYLATION

Abstract: A general method for producing methylol compounds by the reaction of an organometallic compound with formaldehyde in which the formaldehyde is generated in situ from and by the use of a high molecular weight linear formaldehyde homopolymer.

Description: PROCESS FOR HYDRO.XYMETHYLATION This invention is in the field of chemical pro¬ cesses and relates to a method for hydroxymethylating organic substrates to produce hydroxymethyl deriva- tives thereof, sometimes referred to herein as ■• methylol" compounds or "carbinols". In particular, the present invention pertains to a process for pro¬ ducing methylol compounds by the reaction of an organometallic compound with formaldehyde produced ITL situ from a high molecular weight linear formaldehyde homopolymer. Methylol compounds of various structures abound in the chemical literature. Many such compounds are useful end-products in themselves, while others are useful as intermediates in the preparation of various useful end-products. For example, certain substi- tuted-phenylmethyl alcohols, such as the various biphenylmethanols disclosed in U.S. Patent Nos. 4,130,657; 4,214,004; 4,329,518; and 4,402,973 are useful intermediates for insecticidal pyrethroid esters. A number of methods for producing methylol com¬ pounds are available to the chemical practitioner. For compounds having one or more active carbon-bonded protons, capable of being removed by a base, and for halogen-containing compounds from which Grignard reagents can be produced, the usual method for intro¬ ducing a hydroxymethyl group into the molecule, in place of the active hydrogen or the halogen, is b reaction of the Grignard reagent or a metal salt of the organic substrate with formaldehyde. This general method is illustrated in the following chemical equa¬ tion in which R is an organic radical such as a hydro- carbyl radical and M is a metal or metal-halide_ R-M + CH 2 0 -> RCH 2 0H. Where the carbon-bonded active proton of the organic substrate is highly acidic, for ex : araple, the α protons of diethyl malonate, the hydroxymethylation reaction may be conducted simply and conveniently in water in the presence of a base such as potassium bicarbonate, the formaldehyde reactant being commer¬ cially available as an aqueous solution. However, for Grignard or similar hydroxymethyla¬ tion reactions where the organometallic substrate is subject to decomposition by water, generally where the pK, value for the organometallic material is lower than about -5, the use of aqueous formaldehyde is contraindicated. In such cases precautions must be taken to exclude water from the reaction mixture to preserve the integrity of the organometallic substrate for reaction with the formaldehyde. Generally, the • formaldehyde reactant is generated from the solid polymer paraformaldehyde which depolymerizes or "unzips" to produce formaldehyde vapors. The depoly- merization is facilitated by heat and is usually accomplished either i_n situ on heating the reaction * mixture containing the paraformaldehyde or by pyrolyz- ing the para ormaldehyde in a separate vessel and conducting the vapors so produced into the hydroxy¬ methylation reaction vessel. The use of parafor aldehyd.e directly as a source of dry formaldehyde, however, has not been entirely satisfactory inasmuch as paraformaldehyde itself is not anhydrous, but contains a certain amount of free water in addition to the chemically combined water that is part of the paraformaldehyde molecule itself and is released in the unzipping process. • The Kirk- Othmer Encyclopedia of Chemical Technology, 3rd ed; John Wiley ξ Sons, New York, 1978; Vol. 11; page 247 states that commercial paraformaldehyde (average mole¬ cular weight of about 600) in powder form contains up to 5% free and combined water and in flake form, up to 9%. Thus, use of commercial paraformaldehyde as such in a Grignard or similar organometallic hydroxymethyl- ation reaction as a source of the requisite formalde¬ hyde may result in the inclusion in the reaction mixture of up to 5% or more of water and the destruc- tion of an equivalent amount of the organometallic reagent. While formaldehyde vapors may be generated by the pyrolysis of paraformaldehyde outside the hydroxy- methylation reaction vessel and subjected to appropri- ate drying conditions prior to bringing it into • contact with the organometallic substrate, such a method adds*an additional step to the hydroxymethyla- tion process and may unduly subject the worker and other nearby personnel to the possibility of coming into contact with formaldehyde vapor or dust which is highly irritating, particularly to the eyes and respiratory tract, and may cause skin sensitization or dermatitis. The present invention represents an improvement over the prior art method of hydroxymethylatioh in that an inherently drier source of formaldehyde than previously used is employed in the present process thereby reducing aqueous decomposition of the organo¬ metallic substrate and allowing ,for increased yields of the desired carbinol products. Furthermore, the present high molecular weight linear formaldehyde homopolymer, like paraformaldehyde, may be added directly to the reaction mixture allowing the formal¬ dehyde being formed to be consumed in the desired reaction concomitantly with its formation, thereby reducing the risk to personnel of exposure to formal¬ dehyde fumes. In the present invention, the requisite formalde¬ hyde is generated iτι situ from and by the use of a high molecular weight linear formaldehyde homopoly- mer. The high molecular weight formaldehyde homopoly- mers useful in the present invention are polyoxy- methylene compounds having a molecular weight of at least about 10,000. The polymers are composed of repeating oxymethylene units which form a linear acetal chain -—0-CH 2 -0-CH 2 '-' and are terminated at each end by a hydroxy group or by a labile end-capping group such as an ester group, or are terminated at one end by a non-labile end-capping group such as an ether group and at the other end by a labile end-capping group. Polymers that are capped at only one end, by a labile or a non-labile end-capping group, are also useful in the present process and are within the scope of the present invention. Labile end-capping groups are groups that are removable under the conditions of the hydroxymethylation process, whereas non-labile groups are not removable under such conditions. In order for a formaldehyde homopolymer of appropriate molecular weight to be capable of being depolymerized or unzipped to produce formaldehyde under typical hydroxymethylation process conditions and, therefore, to be suitable for use in the present process, it is necessary that at least one terminal of the formalde¬ hyde polymer be occupied by a hydroxy group or a labile end-capping group. It is well known in the art of polymer chemistry, as disclosed in U.S. Patent No. 2,964,500, that polymer compositions, by virtue of limitations inher¬ ent in the methods known and used in the art for producing them, are not homogeneous but are mixtures of molecules of various molecular weights generally concentrated within a narrow range. Polymer composi¬ tions are .also inexact with respect to end-caps. For example, in a composition of polymers having an ether group or an ester group at one end and a hydroxy group at the other, a small portion of the composition will likely consist of polymers capped at both ends as well as completely uncapped polymers. Therefore, it will be understood that molecular weights recited herein for formaldehyde polymers useful in the present process are average molecular weights and that some small portion of the polymer composition may differ from the major portion of the composition. The limitations described herein to define the formalde- hyde polymers suitable for use in the present process are fully met if met by the polymers which constitute the major portion of a polymer composition. The formaldehyde homopolymers useful herein may have an average molecular weight up to about 1,000,000 or higher. The average molecular weight will usually be in the range of 10,000 to 200,000, preferably in the range of 15,000 to 150,000, and more preferable in the range of 20,000 to 100,000. Those materials having an average molecular weight in the range of about 25,000 to 75,000 are especially preferred. Included among this last group of preferred polymers • are polyoxymethylene diacetates such as the Delrin brand of acetal horaopolymer resins sold by E.I. du Pont de Nemours § Co., Inc., Wilmington, Delaware. Polyoxymethylene diacetates having an average mole¬ cular weight of about 50,000, such as Delrin 500, are particularly desirable. Suitable formaldehyde poly¬ mers are also described in various patents and litera¬ ture in the art. Both the polyoxymethylene glycol starting materials and diacetate products described in U.S. Patent 2,964,500, as well as the polyoxymethylene products described in U.S. Patents 2,768,994; 2,828,286; 2,841,570; and 2,848,437, all of which patents are incorporated herein by reference, are suitable for use in the present process. The polyoxy¬ methylene products disclosed in U.S. Patent No. 2,844,561, incorporated herein by reference, and which have incorporated in their structures a small amount of an amine polymerization initiator are also gener- ally useful in the present invention but are not preferred. Other references disclosing the prepara¬ tion and properties of high molecular weight formalde¬ hyde homopolymers, including materials useful herein, are "The Kirk-Othmer Encyclopedia of Chemical Tech- nology", 3rd ed. ; John Wiley § Sons, New York; 1978; Vol. 1; pages 112-123 and "Formaldehyde"; ACS Mono¬ graph Series; J. Frederic Walker, Ed.; 3rd ed; Rein- hold Publishing Corp., New York; 1964; Chapter 7. " The high molecular weight linear, formaldehyde polymers useful in the present invention are compounds of the formula R 1 0-CCH 7 0) n -R 2 I wherein R 1 and R2 are independently hydrogen or an end-cap group that is removable under the conditions employed in the hydroxymethylation process. One of R 1 and R2, but not both, may also be a group that is not removable under the hydroxymethylation condi- tions. Thus, either uncapped or certain end-capped polymers may be used. Uncapped formaldehyde polymers and polymers capped at only one terminal may depolymerize on stand¬ ing to release formaldehyde. As with paraformalde- hyde, depolymerization of the higher molecular weight uncapped or partially capped polymers useful herein is facilitated by heat. HOCH 2 CH 2 0(CH 2 0) n H —-— • n CH 2 0 + HOCH 2 CH 2 OH H0CCH 2 0) n H • > n CH 2 0 + H 2 0 Formaldehyde polymers end-capped at both terminals offer an advantage over the corresponding uncapped materials in that they are storage-stable and will not depolymerize to release formaldehyde fumes until removal of at least one of the end-caps. End-caps that are not removable under hydroxy¬ methylation process conditions, and which may be present at one terminal but not both, include typical ether forming groups such as alkyl, aryl, and aryl- alkyl radicals and substituted derivatives thereof, for example, methyl, methoxyethyl, hydroxyethyl, hydroxypolyethoxyethyl, methoxypolyethoxyethyl, poly- ethoxyethyl, phenyl, and benzyl. End-caps that are removable under hydroxymethyla¬ tion process conditions include acyl and similar ester forming groups that are reactive themselves toward the organometallic substrate and are ultimately eliminated from the polymer leaving the previously capped end of the molecule uncapped and free to depolymerize. Typical removable end-caps are radicals such as -CQ-R 3 or -P(Q)R R 5 wherein R 3 , R 4 and R 5 indepen¬ dently are optionally substituted alkyl, alkoxy, alkylthio, aryl, aryloxy, arylthio, arylalkyl, aryl- alkoxy, or arylalkylthio and Q is 0 or S. Preferably, 3 4 5 R , R , and R are Independently selected from alkyl, aryl, and arylalkyl each of which may be sub- stituted. " A preferred end-cap (R 1 or R2 or both) is the radical -CO-R , especially -CO-CH j . In a preferred embodiment of the invention, the formalde¬ hyde polymer is a polyoxymethylene diacetate (R = 7 R = -CO-CH,) having an average molecular weight in the range of about 25,000 to 75,000, particularly the material having an average molecular weight of about 50,000. Use of the corresponding glycol (R = R = hydrogen) also represents a preferred embodi¬ ment of the invention. Examples of removable end-caps are radicals such as -C0-CH 3 , -CO-CH(CH 3 ) 2 , -CO-CH(CH 2 ) 4 CH 2 ., -C0-C 6 H 5 , -CO-CH 2 C 6 H 5 , -CS-CH 3 , -C0 2 CH 3 , -CS 2 CH 3 , -C0-CF 3 , -C0-SCH 3 , -C0 2 C 6 __ 5 , -C0 2 CH 2 C 6 H 5 , -P(0)(CH 3 ) 2 , -P(S)(CH 3 )(SC 2 H 5 ), -P(0)(OC 2 H 5 ) 2 , -P(S)(CH 3 )(OC 2 H 5 ), and -P(0)(C 6 H 5 )(OC 2 H 5 ). Any alkyl or aryl substituent or portion of a substituent herein may be substituted, for example, with halogen such as fluorine, chlorine, or bromine, cy ' ano, nitro, hydroxy, alkoxy, alkylthio, or the like. Additionally, any aryl group may be substituted with alkyl. Any alkyl may be a straight chain, branched chain, or cyclic radical, frequently a lower alkyl of 1 to 8 (preferably 1 to 4) carbon atoms. Any aryl group herein may be a hydrocarbyl radical such as phenyl or a heteroaryl radical, for example, furyl, thienyl, pyridyl, pyrimidyl, oxazolyl, pyrrolyl, isoxazolyl, thiazolyl, or isothiazolyl. Halogenated alkyl or aryl groups may have one or more same or different halogen atoms. The high molecular weight formaldehyde polymers described above are useful as a source of formaldehyde reactant in hydroxymethylation processes in which an organometallic substrate is reacted with formaldehyde to produce a methylol compound. Since the present polymers represent a source of substantially anhydrous formaldehyde, they are especially useful in those instances where the organometallic substrate is sensi¬ tive to water. The present high molecular weight formaldehyde polymers are pulverulent solids and are advantageously employed in the present process in the form of a fine powder. It is preferred, for increased reaction rates, that the particle size be sufficiently small for the powder to pass through a 300 μm (50 mesh U.S.) sieve. It is desirable, therefore, to pulverize or grind coarser grade material to obtain a fine particle size. The organometallic compound is any compound such as phenylmagnesium chloride or phenyllithium which reacts with formaldehyde under anhydrous hydroxy- methylation conditions to produce a carbinol. For example, the organometallic compound may be an organo- magnesium halide compound or an .organozinc halide compound in which the halide is a chlorine, bromine, or iodine atom, an organolithium compound, an organo- sodium compound, an organopotassium compound, or the like. Frequently, the organometallic compound will be an organomagnesium halide compound. The organic moiety will generally be strongly associated with the metal moiety via an ionic carbon-to-metal bond, although the degree of association will generally vary with the polarity of the solvent used in the hydroxy¬ methylation process. The organic moiety may be aromatic or non-aromatic, it may be a hydrocarbyl radical or contain one or more heteroatoms, and it may or may not have one or more points of unsaturation as, for example, an alkynyl radical R-C≡C-. In a preferred embodiment of the present inven¬ tion, the organometallic substrate is an aryl agnesium halide, for example, a phenylmagnesium halide. Phenylmagnesium halides of particular interest include those of the formula in which X is chlorine, bromine, or iodine and R R 7, and R8 are independently hydrogen, halogen o such as chlorine, or lower alkyl. R may also be phenyl which may be substituted with halogen or lower alkyl. The carbinol products of this embodiment are useful intermediates for insecticidal pyrethroid esters, especially where R. is hydrogen or methyl, more especially hydrogen, R 7 is methyl, and R8 is chlorine or, particularly phenyl. The present process is illustrated for a pre¬ ferred embodiment in the following chemical equation; Ila la III Reaction of the organometallic compound with the poly- oxymethylene diacetate results in the removal of one or both acetyl groups from the formaldehyde polymer, and the resulting polymer product then depoly erizes to generate formaldehyde which reacts with additional organometallic compound to produce the carbinol pro- duct. The present process may be conducted under any reaction conditions that would be acceptable in a hydroxymethylation process involving the reaction of the same organometallic compound with formaldehyde in which the formaldehyde is generated jjr situ from para- ormaldehyde. At least a stoichiometric amount of the formaldehyde polymer, calculated on the basis of the amount of polymerized formaldehyde' present, should be employed. In general, the organometallic compound (produced in situ or separately) is brought into contact with the high molecular weight formaldehyde polymer under substantially anhydrous conditions in the presence of a substantially inert solvent under a substantially inert atmosphere. As with similar organometallic reactions, care should be taken to exclude moisture, oxygen, and carbon dioxide, which may react with the organometallic compound, by using an inert atmosphere such as nitrogen or helium. The reaction may be. conducted under standard temperature conditions for similar reactions, gener¬ ally at a temperature in the range of about 25° to 150°C, advantageously at an elevated temperature such as a temperature of about 60°, preferably up to about 100°C. Frequently, the upper temperature limit will be the boiling point of the solvent or a temperature just below the melting point of the formaldehyde poly¬ mer. Preferably, the insoluble solid formaldehyde polymer is maintained as a fine powder in the reaction mixture to facilitate the generation of formaldehyde. If allowed to melt, the polymer may agglomerate into a gummy mass which may hinder the reaction. Any of the solvents typically used in similar organometallic reactions, such as ethers or hydro- carbon solvents, may be suitably used in the present process. Some organometallic compounds, particularly organosodium compounds, are known in the art to be highly reactive toward diethyl ether, and in such cases, as in the prior art processes, a different solvent should be selected. Tetrahydrofuran is a preferred solvent. As in the prior art hydroxymethylation processes involving the reaction of an organometallic compound with formaldehyde and conducted under anhydrous condi- tions, the carbinols are produced in the present process in the form of complex salts from which the desired carbinols are freed by acid hydrolysis. This involves simply contacting the salt with water and adjusting the pH by the addition of sufficient acid or aςidic material to free the carbinol from the salt. Generally, the reaction mixture is poured over ice and the mixture is made acidic by the addition of an acid such as hydrochloric acid, usually concentrated hydro¬ chloric acid. Where the desired carbinol product is sensitive to strong acids, the hydrolysis will usually be carried out by the addition of an acidic material such as ammonium chloride, generally as a saturated aqueous solution. The present invention is further illustrated in the following example. EXAMPLE SYNTHESIS OF ( 2-METHYL[1,1'-BIPHENYLj-3-YL)METHAN0L A. Preparation of ( 2-methyl[l,1' -biphenyl]- 3-yl)magnesium chloride Under a nitrogen atmosphere, 101.3 g (0.50 mole) of 3-chloro-2-methylbiphenyl (92% purity) in 75 g of dry tetrahydrofuran was added dropwise over two hours ■ with stirring to a gently refluxing mixture of 13.1 g (0.54 mole) of fresh magnesium turnings, the heel from a previous run containing 0.21 mole of unreacted magnesium, and 75 g of dry tetrahydrofuran in a dry reaction vessel. Upon complete addition, the reaction mixture was heated at reflux for five additional hours. Gas chromatographic analysis of a quenched sample of the reaction mixture showed 1.2% of unre- acted 3-chloro-2-methylbiphenyl and 92.4% of 2-methyl- biphenyl. The reaction mixture was allowed to cool overnight. B. Preparation of (2-methyl[l,I' -biphenyl3- 3-yl)methanol Under a nitrogen atmosphere, the reaction mixture from above was decanted into a clean, dry flask, leav¬ ing the unreacted magnesium turnings in the first flask. This solution, which contains (2-methyl[l,1'- biphenyl3-3-yl)magnesium chloride, was heated to reflux, and 16.5 g (0. * 55 mole based on formaldehyde) of polyoxymethylene diacetate (avg. mol. wgt. approx. 50,000, available commercially from E.I. du Pont de Nemours § Co., Inc., Wilmington, Delaware under the trade name Delrin 500 acetal homopolymer resin) , milled to about 80 mesh, was added with stirring over three hours. Refluxing was continued for four addi¬ tional hours after which the reaction mixture was allowed to cool and stand overnight. The mixture was then heated to 53°C and was poured into a mixture of 100 g of ice, 52 g of concentrated hydrochloric acid, and 200 g of a mixture containing 95% ri-octane and 5% toluene (wt/wt). This mixture was filtered and the organic phase separated. The organic solvents were distilled off, boiling range 65-93°C. During a four hour period the solution was cooled with stirring to approximately 5°C and was then filtered. The filter cake was washed with 100 mL of cold n-octane and air-dried for 0.'5 hour. The filter cake was broken up and dried under a vacuum at 55°C for four hours, yielding 78.9 g of (2-methyl[l,l * -biphenyl3-3-yl)- methanol (89.9% purity), a yield of 70.8% of theory.

Claims: Claims: 1. A method for producing a methylol compound by the reaction of an organometallic compound with formaldehyde, characterized by generating the formal- * dehyde jji situ from and by the use of a linear formal¬ dehyde homopolymer having an average molecular weight of at least 10,000. 2. The method of claim 1 characterized in that the formaldehyde polymer is terminated at each end by a hydroxy group or by a labile end-capping group, or is terminated at one end by a non-labile end-capping group and at the other end by a labile end-capping group, or is terminated at one end by a hydroxy group and at the other end by a labile or a non-labile end-capping group. 3. The method of claim 2 characterized in that the ormaldehyde polymer has an " average molecular weight in the range of 10,000 to 200,000. 4. The method of claim 3 characterized in that the labile end-capping group is a labile ester group and the non-labile end-capping group is an ether group. 5. The method of claim 4 characterized in that the formaldehyde polymer is a polymer of the formula R 1 0-(CH 7 0) n -R 2 in which R 1 and R2 are independently hydrogen, a non-labile radical selected from the group consisting of alkyl, aryl, arylalkyl, and substituted derivatives thereof, or a labile radical of the formula -CQ-R or -P(Q)R R in which R , R , and R are independently selected from alkyl, alkoxy, alkylthio, aryl, aryloxy, arylthio, arylalkyl, arylalkoxy, arylalkylthio, and substituted derivatives thereof and Q is oxygen or sulfur, with the proviso that at least one of R and R 2 is hydrogen, -CQ-R 3 , or -P(Q)R 4 R 5 . 6. The method of claim 5 characterized in that for R 1 , R 2 , R 3 , R 4 , and R 5 , any alkyl group or the alkyl portion of any group is lower alkyl or a substituted lower alkyl and any aryl group or the aryl portion of any group is phenyl or a substituted phenyl. 7. The method of claim 6 characterized in that R 1 and R2 are independently selected from hydrogen and a labile radical -C0-R in which R is lower alkyl. 8. The method of claim 7 characterized in that each of R 1 and R2 is hydrogen. 9. The method of claim 7 characterized in that each of R 1 and R is -CO-CH j . 10. The method of claim 8 or 9 characterized in that the organometallic compound is selected from the ' group consisting of an organomagnesium halide com¬ pound, an organozinc halide compound, an organolithium compound, an organosodium compound, and an organo- potassium compound, wherein halide is a chlorine, bromine, or iodine atom. 11. The method of claim 10 characterized in that the organometallic compound is an organomagnesium halide compound. 12. The method of claim 11 characterized in that the organomagnesium halide compound is an arylmagne¬ sium halide compound. 13. The method of claim 12 characterized in that the arylmagnesium halide compound is a phenylmagnesium halide compound and the methylol product is a phenyl- methyl alcohol. 14. The method of claim 13 characterized in that the phenylmagnesium halide compound is a compound of the formula wherein X is chlorine, bromine, or iodine, R and 7 R are independently hydrogen, halogen, or lower g alkyl, and R is hydrogen, halogen, lower alkyl, or phenyl which is unsubstituted or substituted with halogen or lower alkyl, and the methylol product is a phenylmethyl alcohol of the formula o in which R and R are defined as above. 15. The method of claim 14 characterized in that R is hydrogen or methyl, R is methyl, and R is chlorine or phenyl, with the proviso that when R is chlorine R is hydrogen. 16. The method of claim 15 characterized in that R is hhyyddrrooggeenn.. 17. The method of claim 16 characterized in that R is phenyl. 18. The- method of claim 17 which is conducted under substantially anhydrous conditions, in the presence of a substantially inert atmosphere, at a temperature of 25°C up to a temperature below the melting point of the formaldehyde polymer. 19. The process of claim 18 characterized in that the temperature is in the range of 60° to 100°C. 20. The process of claim 19 characterized in that the formaldehyde polymer has an average molecular weight in the range of 15,000 to 150,000. 21. The method of claim 20 characterized in that the average molecular weight of the formaldehyde poly¬ mer is in the range of 20,000 to 100,000. 22. The method of claim 21 characterized in that the average molecular weight of the formaldehyde poly¬ mer is in the range of 25,000 to 75,000.

Inventors: DELMAR ERIC GEORGE, KWIATKOWSKI CHARLES THOMAS, DELMAR, ERIC, GEORGE, KWIATKOWSKI, CHARLES, THOMAS
Applicants: FMC CORP, FMC CORPORATION
Application year: 1985
Main classification: C07C33
IPC codes: C07B31, C07B41, C07C27, C07C29, C07C33, C07C67, C07F3