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6.2 Epichlorohydrin |
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Reactions with alcohols
The action of alcohols on epichlorohydrin proceeds by addition of the former at the epoxide group in such a manner as to form y-ethers of glycerol amonochlorohydrin-; succeeding reactions may lead to glycidyl ethers, glycerol a-monoethers, or glycerol a,y-diethers. In most instances, by choice of proper reaction conditions and catalyst, any of these products can be obtained in practical conversion and yield. Glycerol a-monochlorohydrin ethers. The lower primary and secondary alcohols combine with epichlorohydrin at moderate temperatures in the presence of acidic catalysts such as sulfuric 59, 69,130 and hydrofluoric 166 acids, boron trifluoride 187, ferric chloride 89, 167, stannic chloride 167, and other metal halides 167 with the formation of glycerol a-monochlorohydrin y-ethers, along with minor amounts of the ß-ethers; stannic chloride is a suitable catalyst for the addition of tertiary alcohols 167. Higher reaction temperatures are required with higher aliphatic and aralkyl alcohols.
SnCl4
CH2 - CH - CH2CI+ROH ----> ROCH2 - CHOH - CH2CI
\ /
O
This reaction may be carried out by reacting four moles of a lower alcohol with one mole of epichlorohydrin in the presence of 0.002 mole of stannic chloride as catalyst. The reaction starts at about 10° to 25°C and heat is evolved which rapidly increases the temperature to the boiling point. Maintenance of the reaction temperature at the boiling point for a few minutes gives yields of about 90 percent. With higher alcohols the reaction is not as rapid and it may be necessary to heat slowly the reaction mixture to increase the temperature to about 900C. Anhydrous conditions must be maintained for best results.
Glycerol a-monochlorohydrin ethers have also been synthesized by heating together alcohols and epichlorohydrin under pressure in the absence of a catalyst 116, 253. Glycidyl ethers. Ethers of glycerol a-monochlorohydrin prepared from the lower alcohols are converted to glycidyl ethers by the action of concentrated aqueous sodium hydroxide solution (30 percent to 50 percent by weig ht) at tem peratu res f rom 0° to 30°C, followed by a short reaction period at 85° to 90°C 56,59. More drastic conditions may be required for the higher ethers, and the use of a solvent may prove helpful.
ROCH2 - CHOH - CH2CI+NaOH -> ROCH2 - CH - CH2
\ /
O
Glycerol a-monoethers. These ethers are conveniently derived by heating the a-monochlorohydrin y-ethers of the lower primary or secondary alcohols at 160°C for one hour with 10 percent sodium bicarbonate solution 206.
NaHCO3
ROCH2 - CHOH - CH2CI+H2O ------>
ROCH2 - CHOH - CH2OH
They can also be prepared by hydrolysis of the corresponding glycidyl ethers. A ten to one molar ratioof water to ether, temperatures of 80° to 100°C for two to four hours, and 0.1 to 0.2 percent by weight sulfuric acid (based on the ether) as catalyst, give good yields of the glycerol a-monoethers. The use of a suitable solvent or emulsifying agent overcomes the difficulty imposed by the limited solubility to glycidyl ethers of the higher alcohols.
H2SO
ROCH2 - CH - CH2+H20 ---->
\ /
O ROCH2 - CHOH - CH2OH
A number of glycerol a-monoethers have been obtained by heating together glycerol a-monochlorohydrin, the alcohol and caustic 58. The monoethyl ether, for example, was prepared in about 75% yield by refluxing a-monochlorohydrin with a large volume of 99% ethanol and a slight excess of anhydrous caustic soda.
Glycerol a,y-diethers. The reaction of glycidyl ethers with alcohols is a very satisfactory means of synthesizing the diethers of glycerol; the method is also particularly suited to the preparation of the mixed alkyl diethers:
acid or
ROCH2 - CH - CH2+R'OH -------> ROCH2 - CHOH - CH2OR'
\ / base
O
The reaction is catalyzed by both acidic and basic substances, although acidic catalysts are preferred 167 and stannic chloride has proven to be one of the most satisfactory catalytic agents. By using a large (10 to 1) excess of alcohol to glycidyl ether to minimize formation of higher molecular weight reaction products, stannic chloride as catalyst, and strictly anhydrous reagents, good yields of the diethers can be obtained. The catalyst can be destroyed by the addition of an alkali carbonate to the reaction mixture before distillation.
The remaining hydroxyl group in the diether can combine also with glycidyl ether, under the same general conditions, to give a diglycerol triether which in turn can react still further to give complex polyethers:
acid or
ROCH2 - CHOH - CH2OR'+ROCH2 - CH - CH2 ------->
\ / base
O
ROCH2
\
CH-0-CH2-CHOH-CH2OR
/
ROCH2
For the intended preparation of these diglycerol triethers, the glycerol diether and the glycidyl ether are combined in the presence of stannic chloride as catalyst 206. A 5:1 ratio of the glycerol diether to the glycidyl compound results in a very good conversions to triether-I with a lower ratio the amount of higher condensation products is substantially increased.
Glycerol diethers of a variety of primary and secondary aliphatic and alicyclic alcohols, and tertiary alcohols (for example, tertiary butyl alcohol) have been synthesized by this procedure 206; the method has also been employed for preparation of mixed alyl-aryl diethers 206. An alternative method for preparing glycerol di ethers of the lower primary alcohols consists in reacting together epichlorohydrin and the alcohol and caustic under anhydrous conditions. In an early preparation 255: see also reference 57 the dimethyl, diethyl, dipropyl, diallyl, and diisoamyl ethers were synthesized by adding epichlorohydrin to the theoretical amount of the alcohol containing 10 percent of potassium hydroxide in solution. This procedure has been advantangeously modified by adding epichlorohydrin to a refluxing solution consisting of a large excess (10 to 1) of the anhydrous alcohol and a slight excess of sodium hydroxide; eighty percent and higher yields of glycerol dimethyl ether have been obtained by this modification, and the yield has been improved still further by substituting sodium methylate for caustic soda 206. Glycerol a,y-dichlorohydrin may be substituted for epichlorohydrin in this procedure 58, 59, utilizing, of course, greater quantities of caustic; with the dichlorohydrin 70 percent and higher yields of the diethyl ether have resulted 58, 206. Attempts to prepare the mono- and di-tert-butyl ethers by reacting tert-butyl alcohol and epichlorohydrin in the presence of sodium hydroxide or sulfuric acid followed by addition of sodium hydroxide have been unsuccessful 105; however, preparation of the di-tert-butyl ether by reacting epichlorohydrin with a 10 percent solution of potassium hydroxide in tert-butyl alcohol has been reported 256. Condensation with polyhydric alcohols. Ethylene glycol and epichlorohydrin in the presence of sulfuric acid form 1-chloro-3-(2'-hydroxyethoxy)-2propanol 128;and themonosodiumsaltof ethylene glycol in glycol solution forms 1,3-bis (2'-hydroxyethoxy)-2-propanol with the epoxide 128. The reaction of epichlorohydrin with monosodium glycerate is reported to form a polymer of the inner anhydride of diglycerol 176, while reaction of epichlorohydrin with glycerol at a higher temperature gives a y-chloro-ß-hydroxypropyl ether of glycerol 152. The condensation of epichlorohydrin with a variety of other polyhydric substances including sorbitol and erythfitol 202, polyglycols and polyglycerols 43, 203, cellulose 46, 168, 186 and its alkyl ethers 47, polysaccharides 60 and polyvinyl alcohol 199, 200 has also been disclosed or suggested. These condensation products are claimed useful in various applications directly, or after treatment with a variety of mono- or poly-functional substances.
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