Abstract:
The aromatic hydroxyl groups of aromatic hydroxyl-containing compounds can be allylated to greater than 95% conversion by reacting the alkali metal salt of said aromatic hydroxyl-containing compounds with an allyl halide such as allyl chloride in the presence of a polar aprotic solvent such as dimethylformamide. These compounds are useful in preparing epoxy resins containing a low halogen content.

Description:
BACKGROUND OF THE INVENTION 
     The present invention pertains to a method for allylating aromatic hydroxyl-containing compounds. The allyl ethers of polyphenols are useful for preparing epoxy compounds low in aliphatic halogen content. 
     Epoxy resins are being used in the electronics industry as components in electrical laminating varnishes, potting compositions encapsulating compositions and the like. Since aliphatic halogen atoms are detrimental to electrical properties, it is desirable to have available for the electronics industry epoxy resins which are extremely low in aliphatic halogen content. The traditional method for preparing aromatic epoxy compounds is to react an aromatic phenolic hydroxyl-containing material with an epihalohydrin and dehydrohalogenating the resultant halohydrin intermediate product with a suitable dehydrohalogenating agent such as an alkali metal hydroxide, carbonate, bicarbonate or the like. However, the resultant epoxy compound usually contains a relatively high amount of aliphatic halogen atoms of either the bound halogen type or the hydrolyzable halogen type or a combination thereof which is often referred to as total halogen content. The aromatic halogen atoms are not usually considered detrimental and are not included in the reporting of the total halogen content since in some instances, such as in electrical laminates, aromatic halogen atoms are desired so as to render the resin more flame retardant. 
     The present invention provides a method for preparing vicinal epoxy compounds which are very low in aliphatic halogen content rendering them particularly suitable for use in the electronics industry. These low halogen content resins are prepared by the peroxide epoxidation of allyl ethers of aromatic compounds which have been prepared by reacting an allyl halide with an alkali metal salt of an aromatic hydroxyl-containing material in the presence of a polar aprotic solvent so as to convert at least 95% of the aromatic hydroxyl groups to allyl ether groups. When protic solvents such as methanol are employed, conversions of not more than about 85% of the aromatic hydroxyl groups to allyl ether groups is obtained. 
     SUMMARY OF THE INVENTION 
     One aspect of the present invention pertains to a process for preparing allyl ethers of aromatic hydroxyl-containing materials which comprises 
     (A) reacting in the essential absence of water other than water produced in the reaction and in the presence of a polar aprotic solvent selected from the group consisting of dimethylformamide, dimethylacetamide, dimethyl sulfoxide, N-methyl pyrrolidinone, tetramethylene sulfone, hexamethyl phosphoramide, and a combination thereof (1) at least one material containing at least one aromatic hydroxyl group with (2) an alkali metal hydroxide, alkali metal carbonate or combination thereof at conditions sufficient to convert at least 95, preferably at least about 98 percent of the aromatic hydroxyl groups to the corresponding alkali metal phenoxide group; 
     (B) reacting the reaction product mixture produced in (A) above with (3) at least one allyl halide at conditions sufficient to convert at least about 95, preferably at least about 98 percent of the alkali metal phenoxide groups to an allyl ether group; and 
     (C) thereafter recovering the resultant allyl ether product. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Suitable aromatic hydroxyl-containing materials which can be employed herein include, for example, those represented by the following formulas I-IV ##STR1## wherein A is a divalent hydrocarbyl group having from 1 to about 25, preferably from 1 to about 10, carbon atoms, a divalent dicyclopentadienyl group, a divalent oligomeric dicyclopentadienyl group, --O--, --S--, --S--S--, ##STR2## each A&#39; is independently a divalent hydrocarbyl group having from 1 to about 25, preferably from 1 to about 10, carbon atoms, a divalent dicyclopentadienyl group or a divalent oligomeric dicyclopentadienyl group; each X is independently hydrogen, a hydrocarbyl or hydrocarbyloxy group having from 1 to about 10, preferably from 1 to about 6, carbon atoms or a halogen atom, preferably chlorine or bromine; X&#39; is a hydroxyl group; X&#34; is a hydroxyl group; Z is hydrogen or a hydrocarbyl group having from 1 to about 10, preferably from 1 to about 6, carbon atoms; each independently has a value from about 1 to about 3; b and c each has a value of zero or 1; each d independently has a value from 1 to 3; the sum of a+b is 4; the sum of d+c is 3; m has an average value from about zero to about 15, preferably from about zero to about 10 and n has a value of zero or 1. 
     The term hydrocarbyl as employed herein includes, alkyl, cycloalkyl, aryl, aralkyl, alkaryl, alkenyl and the like. Likewise, the term hydrocarbyloxy as employed herein includes, alkyloxy, cycloalkyloxy, aryloxy, aralkyloxy, alkaryloxy, alkenyloxy and the like. 
     Particularly suitable aromatic hydroxyl-containing materials include, for example, phenol-formaldehyde novolac resins, o-cresol-formaldehyde novolac resins, p-cresol-formaldehyde novolac resins, resorcinol-formaldehyde novolac resins, combinations thereof and the like. Also suitable aromatic hydroxyl-containing materials include, for example, resorcinol, bisphenol A, bisphenol F, bisphenol K, bisphenol sulfide, bisphenol sulfone, dicyclopentadienyl-bis(2,6-dimethyl phenol), dicyclopentadienyl-bis(o-cresol), dicyclopentadienyl bisphenol, combinations thereof and the like. The polycyclopentadienyl polyphenols and methods for their preparation can be found in U.S. Pat. No. 4,390,680 issued to Donald L. Nelson which is incorporated herein by reference. 
     Also suitable aromatic hydroxyl-containing materials include, for example, 3,3&#39;,5,5&#39;-tetramethyl bisphenol A, 3,3&#39;,5,5&#39;-tetramethyl bisphenol F, 3,3&#39;,5,5&#39;-tetramethyl bisphenol K, 3,3&#39;,5,5&#39;-tetramethyl bisphenol sulfide, 3,3&#39;,5,5&#39;-tetramethyl bisphenol sulfone, 3,3&#39;,5,5&#39;-tetramethyl biphenol, 2,6-dibromo-3,3&#39;,5,5&#39;-tetramethyl bisphenol F, 3,3&#39;,5,5&#39;-tetramethyl-2,2&#39;,6,6&#39;-tetrabromo biphenol, 1,1,1-tri-(hydroxyphenyl)alkanes, combinations thereof and the like. Suitable trihydroxyphenyl alkanes and method for their preparation can be found in U.S. Pat. No. 4,394,496 issued to Paul G. Schrader which is incorporated herein by reference. 
     Suitable alkali metal hydroxides and carbonates which can be employed herein include, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium carbonate, potassium carbonate, combinations thereof and the like. The alkali metal hydroxide is employed in an amount of from about 0.95 to about 5, preferably from about 1 to about 2.5, most preferably from about 1 to about 1.5 moles per aromatic hydroxyl-group contained in the aromatic hydroxyl-containing material. 
     Suitable allyl halides which can be employed herein include, for example, allyl chloride, allyl bromide, allyl iodide, 2-methyl allyl chloride, 2-methyl allyl bromide, combinations thereof and the like. The allyl halide is employed in an amount of from about 0.95 to about 5, preferably from about 1 to about 2.5, most preferably from about 1 to about 1.5 moles per aromatic hydroxyl-group contained in the aromatic hydroxyl-containing material. 
     Suitable aprotic solvents which can be employed herein include, for example, dimethylformamide, dimethylsulfonamide, dimethylsulfoxide, N-methylpyrrolidinone, tetramethylene sulfone, hexamethyl phosphoramide, combinations thereof and the like. 
     The aprotic solvent can be employed in amounts of from about 25 to about 2000, preferably from about 50 to about 1000, most preferably from about 100 to about 500, percent by weight based upon the weight of the aromatic hydroxyl-containing material. 
     The reaction between the alkali metal hydroxide and/or the alkali metal carbonate and the aromatic hydroxyl-containing material can be conducted at any temperature of from about -30° C. to about 120° C., preferably from about 0° C. to about 80° C., at a pressure which does not remove the solvent at the reaction temperature for a time sufficient to convert at least about 95, preferably at least about 98 of the aromatic hydroxyl groups to alkali metal phenoxide groups, usually from about 0.5 to about 20, preferably from about 1 to about 15, most preferably from about 2 to about 10, hours. The reaction between the resultant alkali metal phenoxide and the allyl halide can be conducted at a temperature of from about 0° C. to about 100° C., preferably from about 15° C. to about 60° C., at a pressure which does not remove the solvent at the reaction temperature and for a time sufficient to convert at least about 95, preferably at least about 98 percent of the alkali metal phenoxide groups to allyl groups, usually from about 0.5 to about 20, preferably from about 1 to about 15, most preferably from about 2 to about 10, hours. 
     The allyl ether product can be recovered by any suitable means known to those skilled in the art such as by distillation, water washing, precipitation, extraction, centrifugation, combinations thereof and the like. 
     Epoxidation of the allyl ether groups can be achieved by peroxidation with preformed peracid or by the insitu peroxidation method wherein the material containing the allyl ether groups are reacted with a monocarboxylic acid in the presence of hydrogen peroxide and catalyst at a temperature of from about -40° C. to about 100° C., preferably from about 0° C. to about 80° C., most preferably from about 15° C. to about 70° C. for a time to convert essentially all of the allyl ether groups to glycidyl ether groups, usually from about 2 to about 80, preferably from about 5 to about 48, hours. 
     Suitable peracids include, for example, performic acid, peracetic acid, perbenzoic acid, m-chloroperbenzoic acid, combinations thereof and the like. 
     Suitable monocarboxylic acids include, for example, formic acid, acetic acid, propionic acid, benzoic acid, m-chlorobenzoic acid, combinations thereof and the like. 
     The resultant epoxy resins can be represented by the formulas I, II, III and IV wherein each A, A&#39;, X, Z, a, b, c, d, m and n are as defined above and each X&#39; and X&#34; is a glycidyl ether group. There may be present in the epoxy resin composition, very minor amounts of a material wherein X&#34; is hydroxyl and a portion of the X groups is an allyl group. 
    
    
     The following examples are illustrative of the present invention but are not to be construed as to limiting the scope thereof in any manner. 
     EXAMPLE 1 
     General Procedure 
     To an indicated amount of solvent solution containing an indicated amount of o-cresol novolac resin having an average hydroxyl functionality of 6 was added an indicated amount of solid sodium hydroxide at room temperature (˜25° C.). The mixture was stirred under a nitrogen atmosphere for the time indicated at the temperature indicated. After cooling the solution, the indicated amount of allyl chloride was slowly added at the temperature and over the time indicated. After completion of the allyl chloride, the reaction mixture was digested at the time and temperature indicated. The mixture was then cooled to room temperature (˜25° C.). The solvent was then removed under a vacuum (10 mm Hg) and the indicated quantity of a solvent mixture was added to the syrupy residue. The solution was then washed several times with the indicated quantity of water until the pH was ˜7. The organic layer was separated and concentrated under a vacuum. The yield and selectivity of the resultant allylated o-cresol novolac resin obtained, the reaction conditions, quantities of reactants and results are given in the following Table I. 
     
                       TABLE I______________________________________  A     B       C*       D*     D*______________________________________PREPARA-TION OFALKALIMETALPHEN-OXIDESolventType     DMF.sup.3            DMF     Methanol                           Methanol                                  n-Propanolmilliliters    1000    1200    700    250    500NovolacResingrams    236     236     118    59     59equiv.   2       2       1      0.5    0.5SodiumHydroxidegrams    120     172     86     43     43equiv.   3       4       2      1      1Time, hours    5       4       5-6    4      4, seconds    18,000  14,400  18,000-                           14,400 14,400                    21,600Temperature,    40      40      40-45  40     40°C.ALLY-LATIONREACTIONAllylChloridemilliliters    300     400     200    100    75equiv.   4       4.9     2.45   1.22   1AdditionTemp., °C.    30-35   30-35   30-35  35     45Time, hours    3-4     2       2      2      0.8, sec.   10800-  7200    7200   7200   2880    14400DigestionTemp., °C.    35-40   35-40   35-40  --     --Time, hours    4-6     1       6-8    --     --, sec.   14,400- 3600    21,600-                           --     --    21,600          28,800DigestionTemp., °C.    40-45   40-45   40-45  40-45  55Time, hours    4       5       6-7    1      5, sec.   14,400  18,000  21,600-                           3600   18,000                    25,200DigestionTemp., °C.    55-60   50-55   50-55  50-55  60Time, hours    2-4     3       3      12     6, sec.   7200-   10,800  10,800 43,200 21,600    14,400Solvent mix-ture addedtoluene, gms    500     500     500    500    500methyl ethyl    500     500     500    500    500ketone, gmsWater Wash,    400     400     200    100    100ml/washPRODUCTCHARAC-TERISTICSColor    yellow  yellow  brown  brown  brown    brown   brownViscosity @    4500    5000    4000-  4000-  4000-25° C., cps       5000   5000   5000, Pa · s    4.5     5.0     4-5    4-5    4-5Phenolic OH    &lt;0.03   &lt;0.03   1.34   1.27   1.54content, %Total    &lt;50     &lt;170    --     --     --Chlorine,ppmIonic    &lt;2      &lt;8      --     --     --Chlorine,ppmo-Allylation    &gt;99     &gt;99     75     70     80Components.sup.1,c-Allylation    &lt;1      &lt;1      25     30     18Components.sup.2,%______________________________________ *Not an example of the present invention. .sup.1 oAllylation means that the hydroxyl group was allylated to an ally ether group. .sup.2 cAllylation means that the ring was allylated instead of the hydroxyl group. .sup.3 DMF is dimethylformamide.