GB2077256A - Preparation of methylol ketones and novel methylol ketones - Google Patents

Abstract

Methylol ketones are prepared by a reacting a ketone having from 1 to 6 hydrogen atoms attached to the alpha -carbon atoms thereof, with formaldehyde or a formaldehyde generator or donor in an alkaline reaction mixture having a pH of less than 10 and in the presence of a tertiary amine as catalyst. This process enables novel methylol ketones, that is tri-, tetra-, penta- and hexa-methylol acetone, to be obtained.

Description

SPECIFICATION Preparation of methylol ketones and novel methylol ketones This invention is concerned with a process of preparing methylol ketones by reacting ketones with formaldehyde and/or formaldehyde generators or donors, with certain novel methylol ketones, and with the use of methylol ketones as reactants in the production of polymers.

The reaction between formaldehyde and acetone has been well characterised. As early as 191 1, U.S. Patent 989,993 described the condensation of acetone and formaldehyde in the presence of dilute alkali to form methylol acetone:

Dreyfuss and Drewitt (U.S. Patent 2,387,933) later increased product yield and decreased byproduct formation by using aqueous solvent systems and by maintaining the pH in the range of from 8.5 and 9.5; the product was once again monomethylol acetone.

The preparation of dimethylol acetone is described in U.S. Patent 1,955,060. Dimethylol acetone can occur in unsymmetrical or symmetrical isomers:

unsymmetrical dimethylol acetone symmetrical dimethylol acetone Preparation of dimethylol acetone, in accordance with prior art techniques, involves reacting formaldehyde with acetone in the presence of a strong inorganic alkali catalyst to maintain the pH above 10.0.

The following reaction mechanism is believed to describe the role of the strong alkali catalysts in the methylolation of acetone: 1. Abstraction of hydrogen atom from alpha carbon atom:

2. Reaction of carbanion with formaldehyde:

3. Regeneration of catalyst:

In theory, the above mechanism is repeatable to the extent of substituting up to three molecules of formaldehyde on each alpha-carbon atom of acetone. However, the reaction conditions become more stringent as each additional hydrogen attached to the alpha-carbon atom is replaced by a methylol group.

As indicated, the prior art technique has been, in general, to form methylol-substituted acetone by the reaction of the acetone carbanion with formaldehyde. Stronger alkali is required to form the carbanion as the alpha-carbon atom becomes more highly substituted. Accordingly, only the mono- and di-methylol acetones are known in the prior art. We have now developed a method of preparing methylol ketones which enables tri-, tetra-, penta- and hexa-methylol acetones or ketones to be obtained in addition to the mono- and di-methylol ketones.

As recognized in the prior art, the first hydrogen atom carried by an alpha-carbon atom in a ketone may be readily displaced or substituted. However, further substitution becomes difficult, as indicated schematically below:

(Difficult to Abstract) Specifically, the second and, if present, third hydrogen atoms on the alpha carbon atoms are progressively more difficult to abstract with alkali catalysts. In addition, as the alkali strength is increased, the formation of by-products, such as diacetone alcohol, pinacol, methyl vinyl ether and various cyclic ethers, occurs to an increasingly greater extent.

A critical feature of the present invention is the discovery that tertiary amines enable from one to six molecules of formaldehyde to be substituted on to each molecule of ketone or acetone In using such amines, the reaction pH is kept moderately alkaline, that is, less than 10.0, so that by-product formation is held to a minimum.

According to the present invention, therefore, there is provided a process of preparing a methylol ketone, which comprises reacting a ketone having from 1 to 6 hydrogen atoms attached to the a- carbon atoms thereof, with formaldehyde or a formaldehyde generator or donor in an alkaline reaction mixture having a pH of less than 10 and in the presence of a tertiary amine as catalyst.

While the mechanism of the reactions involved has not been conclusively established, it is believed that the tertiary amine catalyst complexes with a hydrogen atom attached to an alpha-carbon atom of acetone or other ketone; the following is an illustration of the mechanism believed to be involved:

where R is an organic group, the three R groups being the same or different.

The formaldehyde molecule is also partially polarized because of unshared pairs of electrons on its carbonyl oxygen:

The various partial charges can then facilitate reaction between the partially positive formaldehyde carbon and the partially negative alpha carbon on acetone in accordance with the following mechanism:

Illustration of partial charges, product formation.

The tertiary amine thus helps to polarize the acetone alpha carbon and helps to coordinate the reactants for subsequent covalent bonding.

Examples of compounds which can be made by the process of the present invention are given below by way of illustration:

Common Common IUPAC Terminology Structure Terminology 0 3-keto-n-butanol HO-CH2-CH2-C-CH2 mono-methylol (M.W, 8 acetone 0 3-keto-n-pentane-1,5- HO-CH2-CH2-C-CH2-CH 2-OH sym. dimethylol diol (M.W. 118) acetone 3-keto-2ghydroxy- HO-CH2 0 unsym. dimethylol methyl)-butan-1-ol I II acetone (M.W. 118) oCHCCH3 HOCH2 3-keto-2-(hydroxy 0 CH2-OH 1,1 ,3-trimethylol methyl)-pentane-1 || / adetorie 5-diol (M.W. 148) HO-CH2-CH2-C-CH CH2-OH 3-keto-2,2-di- o CH2OH (hydroxymethyl)- II 1 ,1 ,1-trimethylol butane-1 ol CH3-CC-CH2OH acetone (M.W. 148) CH2OH 3-keto2,4-di- HOCH2 O CH2OH sym. tetramethylol (hydroxymethyl)- I tI / acetone pentane-l ,5-diol CH-C-CH (MW. 178) HOCH2 CH2OH 3-keto-2 2-di- O CH20H (hydroxymethy I)- Ol pentane4 ,Sdiol HOCH2-CH2---CH2-OH 1 ,1 ,1 ,3 (M.W. 178) ≈ tetramethylol CH2 OH acetone 3-keto2 ,2-tri- HOCH2 H O CH2OH (hydroxy methy I) \ I e pentane-1 ,5-diol C -C C- 2OH pentamethylol (M.W. 206) / \ acetone HOCH2 CH2OH 3-keto-2,2,4,4- HOH2C O CH2OH tetra(hydroxy- If methyl) -pentane - HOH2C-C-C-C-C H2OH hexamethylol 1 ,Sdiol (M.W. 238) / \e acetone HOH C CH2CH r Of these compounds, trimethylol acetone, tetramethylol acetone, pentamethylol acetone and hexamethylol acetone are novel and constitute a further aspect of the present invention.

In order that the invention may be more fully understood, the following examples are given by way of illustration only: EXAMPLE I To a reaction vessel equipped for heating, cooling and agitation, there were added: Acetone 7.5 mols Formaldehyde 30 mols Triethylamine 0.25 mol The resulting solution was stirred well, heated to 500C and held at 500C for one hour. A further 0.50 mol of triethylamine was then added and the mixture was refluxed at atmospheric pressure for 45 minutes and then cooled to room temperature. The resulting product had a solids content of 53%, a viscosity of 32 centipoises, a pH of 8.75, and exhibited infinite water dilutability. The solid product, tetramethylol acetone containing 2% of unreacted formaldehyde, had a specific gravity of 1.1340.

Tri-, penta- and hexa-methylol-substituted acetones are obtained by using the appropriate stoichiometric quantities of formaldehyde and acetone.

The acetone used need not be anhydrous and experiments have established that the reaction mixture can contain 50% or more of water.

In addition to pure formaldehyde, the various forms of formaldehyde can equally be used, including paraformaldehyde and standard preparations containing 65%, 55%, 45% or 37% or methanol - inhibited formaldehyde solution or any other suitable formaldehyde donor.

The preferred tertiary amine for use in the process according to the invention is triethylamine, but other tertiary amines can equally be used. In principle any tertiary amine having alkyl, aryl or a combination of alkyl and aryl substitutents can be used, for example N-methyl morpholine, dimethyl aniline, trimethylamine, N,N-dimethyl-toluidine and methyldiethylamine.

As already indicated, we have found that such tertiary amines are more efficient than inorganic alkalies in driving the reaction to completion. Indeed, the use of triethylamine makes the reaction very exothermic and gives yields of 95% or better of the desired compounds based on the formaldehyde consumed.

In contrast, it has been found that inorganic bases, such as sodium hydroxide, barium hydroxide, calcium hydroxide and lithium hydroxide, and alkali metal and alkaline earth metal carbonates, or primary or secondary amines, such as ammonia or diethylamine, are not efficient catalysts or effective to drive the reaction to the desired end. Triethanolamine has also been found not to drive the reaction to completion.

The reaction between acetone and formaldehyde catalyzed by triethylamine in a quantity sufficient to maintain a minimum pH of 8.6, can be completed in a time of from 20 minutes to about four hours, depending upon the reaction temperature. The latter is suitably from 400C to 1 200 C. As the substitution of the formaldehyde progresses, the boiiing point of the reaction mixture increases and the reaction temperature can be increased progressively, allowing the reaction to be completed more rapidly.

While the reaction has been described with reference to acetone and formaldehyde as the reactants, those skilled in the art will appreciate that other ketones and other sources of the methylol group (-CH2-OH) may be used.

EXAMPLE II The tetramethylol product of Example I was mixed with a phenol-formaldehyde resol to form a 1:4 weight ratio mixture: phenol-formaldehyde (67% solids) 2400 g tetramethylol acetone (53% solids) 800 g This mixture was then dehydrated to provide a system having the following characteristics.

Viscosity 330 cps Specific Gravity 1.2072 Stroke cure (1 500C) 179 secs.

Sunshine gel (1 350C) 522 secs.

pH 8.5 ASTM Solids (1350C) 65% The utility of the resulting mixture was found to be two-fold. The tetramethylol acetone replaced the conventional and customary methanol solvent needed to solvate the phenoi-formaldehyde resol.

Also, the tetramethylol acetone functions not only as a solvent for the phenolformaldehyde system, but also reacts with the system itself to become a component constituent thereof rather than being flashed off as the methanol would be.

The use of tetramethylol acetone as a "solvent" as opposed to methanol may, depending upon the solubility of the polymerizing agent, yield a reaction system that is further dilutable with water. This obviates the need to use the usual volatile organic diluents or solvents: this greatly reduces the fire hazard and effectively eliminates the atmospheric pollution associated with the use of conventional organic solvents.

The methylol and polymethylol ketones of the invention have been found to have a broad range of utilities: 1. As chemically reactive, co-polymerizable diluents for use with phenol-formaldehyde resins, melamine-formaldehyde resins, urea-formaldehyde resins, xylenol-formaldehyde resins, naphtholformaldehyde resins, aniline-formaldehyde resins, dicyandiamide-formaldehyde resins, furfuryl alcohol formaldehyde resins, furfuraldehyde-phenol resins, cresol-formaldehyde resins, diphenol oxideformaldehyde resins, bis-phenol-formaldehyde resins, benzoguanimine-formaldehyde resins, quinoneformaldehyde resins, hydroquinone-formaldehyde resins, furan-formaldehyde resins, epoxy resins, nylon resins, polyester resins, polyvinyl alcohol resins, resorcinol-formaldehyde resins, aromatic and aliphatic substituted phenol-formaldehyde resins, and silicones; 2.As co-reactants or curing agents for epoxy resins; 3. As chemically reactive polyols which can be reacted with isocyanate compounds to form polyurethane coatings, adhesives or foams, the low content of ionic species in the methylol ketone due to the use of a tertiary amine catalyst ensuring compatability with isocyanate compounds; 4. As reactants with organic acids or acid anhydrides to form polyester resins useful as coatings, moulding compounds, adhesives or foams; 5. As replacements for polyols, such as pentaerythritol, trimethylol propane, ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol or polyethylene glycol.

6. In alkyds, the methylol ketones are useful as a replacement for glycerol or related polyols for coatings and binders; 7. For compounding with phosphorous, sulphur, halogen or nitrogen-containing substances for use as flame retardants.

Thus the methylol ketones may be copolymerized or reacted with such cross-linking compounds as isocyanates, blocked isocyanates, polyisocyanates, organic and inorganic acids, anhydrides, amines and amides, and may be reacted with hydroxyl-containing compounds, such as alcohols, glycols, and polyols, and, generally, with monomers capable of reacting with an alcoholic hydrogen.

Claims (1)

1. A process of preparing a methylol ketone, which comprises reacting a ketone having from 1 to 6 hydrogen atoms attached to the a-carbon atoms thereof, with formaldehyde or a formaldehyde generator or donor in an alkaline reaction mixture having a pH of less than 10 and in the presence of a tertiary amine as catalyst.

2. A process according to claim 1, in which the ketone is acetone.

3. A process according to claim 1 or 2, in which the tertiary amine is triethylamine.

4. A process according to claim 1 or 2, in which the tertiary amine is N-methyl morpholine, diemthyl aniline, trimethylamine, N,N-dimethyltoluidine or methyldiethylamine.

5. Trimethylol acetone.

6. Tetramethylol acetone.

7. Pentamethylol acetone.

8. Hexamethylol acetone.

9. A method of preparing a polymer, which comprises reacting a methylol ketone prepared as claimed in any of claims 1 to 4 or as claimed in any of claims 5 to 8, with an organic or inorganic monomer capable of reacting with alcoholic hydrogen.

1 0. A method according to claim 9, in which the monomer is an isocyanate, blocked isocyanate, polyisocyanate, an organic or inorganic acid, anhydride, amine, or amide.

1 A method according to claim 9, in which the monomer is an alcohol, glycol or polyol.

1 2. A process of preparing a methylol ketone substantially as herein described in Example I.

13. A process of preparing a polymer substantially as herein described in Example II.

14. A methylol ketone when prepared by the process claimed in any of claims 1 to 4 and 12.