CA1047539A - Process for the manufacture of glycol ether formals - Google Patents

Abstract

PROCESS FOR THE MANUFACTURE OF GLYCOL ETHER FORMALS

Abstract of the Disclosure:
Ethylene glycol monomethyl ether formals of the formula [CH3O(CH2CH2O)n]2CH2 in which n is in the range of from 1 to 8, are obtained by reacting at least one ethylene glycol mono-ethyl ether with a 20 to 60 % by weight aqueous formaldehyde solution in the presence of an aliphatic chloro- or chloro--fluoro-hydrocarbon having a boiling point of from 35 to 125°
C at atmospheric pressure and in the presence of a strong acid having a pK value of less than 4 as catalyst, and distilling off the water in the form of an azeotropic mixture.

Description

1()4753~ ~OE 74/F 033 -~his invention relates to a process for the manufacture of formals, i.e. acetals of formaldehyde, of the formula ~H~O(CH2CH20)n~2CH2 by reacting ethylene glycol monomethyl ethers, or more simply "glycol monoethersl', of the general formula CH30(CH2CH20)nH in which n is in the range of from 1 to 8 with aqueous formaldehyde solutions in the presence of acid catalysts.
It is known to react alcohols and in particular glycol monoethers having a primary alcohol function with paraformal-dehyde or more advantageously with trioxane (cf. German Patent 1,293,143) to obtain formals. The two substances yiel-ding formaldeh,yde are prepared from aqueous formaldehyde so-lutions as obtained in the industrial manufacture of formal-dehyde by oxidation of methanol by at least one further pro-cess step. Hence, paraformaldehyde and trioxane are less economic starting materials for making formals than an aqueous formaldehyde solution.
However, the literature indicates various disadvantages for the manu~acture of formals from alcohols and,aqueous for-maldehyde solutions. According to ~.Meerwein in Houben-Weyl, Methoden der Org. Chemie, 4th edition, Stuttgart 1965, volume VI/~, page 210 attemps to remove water by azeotropic dis-tillation resulted in an incomplete separation or no separa-tion at all because of the distillation of a water-alco-hol-aldehyde mixture. ~o dehydrate the distillate drying agents have been proposed, for example calcium carbide, anhy-27 drous cupric sulfate or calcium chloride. ~his method is ~o47539 ~OE 7~/F 033 complicated, considerable amounts Or salt solutions are ob-tained from which products which have distilled over, such as formaldehyde and alcohols, must be separated and rec~cled in-t~ the reaction with the catalyst.
An attempt to react ethylene glycol monomethyl ether with aqueous formaldehyde solution in the presence of an acid catalyst confirmed the aforesaid fact, i.e. the distillate consisted of a water-glycol monoether-formaldehyde mixture.
~he use of benzene, toluene, or heptane as water entrainer chan~ed little in the quantitative composition of the distil-iate.
In the manufacture of formals generally strong acids are used as catalysts, for example H2S04, HCl, p-toluene-sulfonic acid and the like, as well as ~ewis acids such as ~eCi3. Acid ion exchangers have also been proposed (cf. US Patent 2,566, 599). With their use and with a 4 to 5 molar excess of, for example, butanol, a yield of 64 mole % of butano1 formal, calculated on paraformaldehyde, can be obtained.
According to German Patent 1,293,14~ trioxane can be reacted, in the presence of an acid ion exchanger, with a 6 to 9 fold excess of an alcohol, calculated on the trioxane, i.e. a 2 to 3 fold excess of the formaldehyde content of the trioxane~with a selectivity of approximately 90 mole ,b, cal-culated on the alcohol.
~ence, it follows that, inspite of the use of very dif-ferent acid cataiysts, satisfactory selectivities c~n only be obtained when an excess of alcohol is used, so that lar~e 28 amounts of alcohol must be recycled. ~his fact and the hi~h 4~7539 H0~ 74/F 033 price of the starting products for the formaldeh~de, i.e.
paraformaldehyde or trioxane, detrimentally affect the eco-nomy of the above manufacturing processes.
It is the object of the present invention to provide a process for the manufacture of eth~lene glycol monomethyl ether formals of the formula ~CH30(CH2CH20) ~2C~2 in which n is in the range of from 1 to 8, by reacting the correspon-ding ethylene glycol monoethyl ethers with formaldehyde in the presence of an acid catalyst, which comprises reacting one or several ethylene glycol monomethyl ethers with an aqueous for-maldehyde solution of 20 to 60 % strength by weight in the presence of an aliphatic chloro- or chloro-fluoro-hydrocarbon boiling at a temperature of from 35 to 125C at atmospheric pressure and in the presence of 0.2 to 20 G~o by weight, calcu-lated on the glycol monoether(s), of a strong acid ha~ing a pK ~alue below 4 as catalyst, and distilling off the water in the form of an azeotropic mixture.
~he advantages of the claimed process reside in the fact that the most economic substance yisldin~ formaldehyde can be used, i.e. an aqueous formaldehyde solution, and that the ~is-advantages of distilled over reaction components are avoided.
Above all, the process of the invention gives high yields o~
formals even with the use of stoichiometric amounts of the reaction components.
A further surprising advantage is obtai~ed by the use of the chloro- or chloro-fluoro-hydrocarbons as auxiliaries. I~
is known that ethylene glycol monomethyl ether CH30CH2CH20E
28 forms an azeotropic mixture t~ith ;later (15.3 ,~ by ~eight in . .. . . . . . .. ... . . . ...

1~4 7539 ~OE 74/F 033 admixture with water) on the compositon of which commonly used entrainers, such as benzene, toluene, or aliphatic hydrocar-bons, for example heptane, have hardly any influence.
As reported in Houben-~leyl, Methoden der Org. Chemie, volume I/1, Stuttgart 1958, page 867 there are neither sub-stances which are suitable separating aids for all binary azeotropes nor is there a method by which suGh a substance can be determined a priori for a given mixture.
It is, therefore, surprising that the chloro- and chloro--fluorohydrocarbons, in addition to their known property as entrainer, do have a separating effect on the three component system formaldehyde-glycol monoether-water, that is to say, with their use the aqueous distillate is practically free from glycol monoether.
On principle, suitable chloro- and chloro-fluoro-hydro-carbons are all those the boiling point of which at atmos-pheric pressure is in the range of from ~5 to 125C, such as for example di-, tri-, or tetra-chloromethane, ethylene di-chloride, 1,1,2-trichloroethane, 1,1,2-trichlorotrifluoro-ethane, tetrachloroethylene, isopropyl chloride, propyl chlo-ride, propylene dichloride, butyl chloride. Especially pre~
ferred are di-, tri- and tetra-chloromethane since they have a low azeotropic boiling point with water and a low proper boiling point, a sufficient content water in the azeotrope and are readily available on an industrial scale.
- ~he relatively low boiling chloro- and chloro-fluoro-hydrocarbons, ~lhich can be used in the process of the inven-28 tion, have the advantage that only a small proportion of ~ HOE 74/F 033 10~7539 formaldehyde escapes from the reac~ion mixture by distilling out of the equilibrium with its hydrate form.
Suitable glycol monoethers of the above formula to be used for the reaction are the monomethyl ethers of mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, and octa-ethylene glycol.
~hese monoethers can be readily obtained on an industrial scale by a catalyzed reaction of methanol with the correspon-ding and different amounts of ethylene oxide. ~hey can be used either in the form of a uniform substance or in the form of mixtures.
~ he formals obtained by the process of the invention can be used, for example, as stabilizers for acrylonitrile poly-mers or as solvents for making cellulose ester or ether lac-quers. ~hey are also suitable startirlg materials for the pre-paration of dimethyl ethers of the glycols.
In the process in accordance with the invention the pro-portion by weight of the chloro- or chloro-fluoro-hydrocar-bons, used as entrainer and separating aid, to the glycol monoether(s) can vary within wide limits, for example in the range of from 0.2 : 1 to 5 : 1, preferably 0.5 : 1 to 3 : 1.
In general, the formaldehyde and the glycol monoether axe used in stoichiometric proportions, i.e. 1 mole of formal-dehyde for 2 moles of glycol monoether. ~hen, for the further use of the glycol monoether formal the quantitative absence of either formaldehyde or glycol monoether is reauired, the glycol or the aldehyde components should be used in a slight excess, for example from 10 to 20 mole %, so that owing to 28 the very selective and cpmplete reaction a distillation of - ~ . ~, 1~47539 HOE 74/F 033 the glycol monoether formals which, in the case of higher formals with n greater than 3 would cause losses by thermal decomposition, can be dispensed with.
Suitable strong acids having a pK value below 4 are nineral acids or aliphatic or aromatic sulfonic acids, such as sulfuric acid, hydrochloric acid, phosphoric acid, p-tolu-ene-sulfonic acid, or naphthalene-sulfonic acid. Because of the easy handling of a heterogeneous acid catalyst and owing to the fact that cation exchangers do not haYe a corrosive effect, strongly acid cross~inked sulfonic acid group-con-taining polystyrenes are particularly suitable as catalysts.
~hey are generally used in the form of spheres having a dia-meter of from 0.2 to 2 mm. Suitable strongly acid commercial ion exchangers are, for example Amberlyst~ 15 (Rohm & ~aas, ~5 Philadelphia, USA) or ~ewatit~ S 100 (Bayer, Germany). Further suitable strongly acid ion exchangers are listed by E.Dorfner in "Ionenaustauscher", Berlin 1964, pages 15 - 31.
~ he amount of the strongly acid ion exchanger to be used, calculated on the glycolmonoether(s), ranges from 0.2 to 20 and preferably 0.5 to 10 % by weight.
Depending on the mixing ratio, the reaction temperature in the reaction mixture of glycol monoether, aqueous formal-dehyde and chloro- or chloro-fluoro-hydrocarbon is normally in the range of from 40 to 125C with reflux of the halo-hydrocarbon or its azeotrope with water. ~he reaction tempe-rature should be preferably below 100C to keep as low as possible the loss of formaldehyde by distillation out of the 28 reaction mixture. ~his can be reached, :Lor example, by in-~,, 1-)47539 HOE 74/~ 033 creasin~ the proportion by weight of the halohydrocarbon to the glycol monoether, for example from 0.5 : 1 to 3 : 1.
~ o carry out the reaction the components glycol mono-ether and aqueous formaldehyde solution are usually heated in a reaction vessel as commonly used, for example a flask or vessel with stirrer, to boiling temperature together witn the halohydrocarbon and the acid catalyst. ~he water origina-ting from the formaldehyde solution and the reaction ~ater are separated with the aid of a water separator in the form of an azeotropic mixture with the halohydrocarbon. ~he halohydro-carbon is recycled into the reaction vessel. It proved ad-vantageous to install, between the reaction vessel and the water separator, a rectifyin~ column in order to reduce the formaldehyde content in the azeotrope.
~nothe~ advantageous mode of carr~in~ out the reaction consists in boilin~ with reflux the glycol monoether together with the catalyst and a halohydrocarbon and introducing the aqueous formaldehyde solution continuously in dosed quanti-ties. A low formaldehyde partial pressure in the reaction vessel results in a smaller dischar~e of formaldehyde in the aqueous distillate.
~ he parametersfor conversion, selectivity and yield used in the follol~ing examples are defined as follows:
The conversion of the components used, that is to say glycol monoether(s) and formaldehyde is the percentage in moles of reacted component calculated on used component.
The selectivity of a formal is its molar amount in per-28 cent, calculated on one reacted component~

~ 8 --~ . .

~ - EOE 74~F 033 ',. 47539 ~he yield of a formal is its molar amount in percent, calculated on the quantity of one of the components used.
~he following examples illustrate the invention.
x a m p 1 e 760 g = 10 moles of ethylene glycol monomethyl ether, 500 ml of chloroform and 100 g of an acid ion exchanger (Amberlyst~ 15) were heated while stirring in a 2 liter three-necked flask provided with stirrer, dropping funnel and a water separator for use of an entrainer having a den-sity greater than 1. ~he proportion by weight of chloroform to glycol monoether was 0.98 : 1. During the course of 3 hours 405 g of a 37 % aqueous formaldehyde solution, corres-ponding to 150 g or 5 moles of formaldehyde, were uniformly introduced in dosed qu~ltities. While s~irring and ~efluxin~
the water of the formaldehyde solution and the reation water were distilled as an a~eotrope into the water separator over a column havi~g about 2 or 3 theoretical plates, and separa-ted. ~he aqueous distillate contained 10.4 g = 0.34 mole of formaldehyde and no glycol monoether. ~he reaction product contained 4.28 moles of formal of the glycol monoether and 0.93 mole of unreacted glycol monoether.
~he conversion of the glycol monoether was 90.7 mole ,cO, the conversion of the formaldehyde amounted to 93.2 mole ,b.
~he yield of glycol monoether formal ~as 85.5 mole %, corres-ponding to selectivities of 94.5 mole %, calculated on the glycol monoether and 97.4 mole %, calcula-ted on the fornal-27 dehyde.

_ g _ EOE 74/~ 0 ~-~4'7S3~g - E x a m p l e 2 ~he reaction was carried out under the conditions spe-cified in Example 1, but the amou~t of chloroform was re-duced so that its proportion by ~reight to the glycol mono-ether amounted to 0.59 : 1. In this reaction the formaldehyde content in the distillate rose to 0.61 mole. ~he conversion of glycol monoether dropped to 87 mole %.
x a m p l e 3 ~he reaction was carried out as specified in Example 1 with the exception that the chlorofo~m was replaced by 500 ml of carbon tetrachloride (proportion by weight to glycol mono-ether 1.04 : 1). At a sump temperature of initially 70C, which rose to 100C, the glycol monoether l~as reacted to yield the corresponding formal by water separation with the aid of the entrainer. ~he aqueous distillate contained 12.8 g - 0.4~ mole of formaldehyde but no glycol monoether.
When the reaction was repeated with the same starting materials but without use of a column between the reaction flask and the water separator, the formaldehyde content in the aqueous distillate rose to 22.8 g = 0.76 mole. In this case, too, no glycol monoether could be detected in the distillate.
E x a m p l e 4 In a flask 158 g - 2 moles of ethylene glycol monomethyl ether, 81 g of a 37 % aqueous formaldehyde solution, 200 ml - 25 of CH2Cl2, corresponding to a proportion by weight to the glycol monoether of 1.06 : 1 were refluxed, ~hile stirring, 27 in the presence of 1.6 g of Amberlyst$ 15. A packed column HOE 74~F 033 ~r~4~S39 having about 2 to 3 theoretical plates and a water separator were mounted between the 1 liter flask and the reflux con-denser. The water of the formaldehyde solution and the water ~ormed in the reaction were removed as azeo-trope. The tempe-rature of the reaction mixture was in the range of from 50 to 60C. After about 7 hours the reaction was terminated.
~he removed water had a formaldehyde content of 1.05 g =
-0.035 mole. The conversion of the glycol monoether was 93 mole % and the yield of glycol monoether formal amounted to 87.2 mole %, corresponding to a selectivity of 93.7 mole %, calculated on the glycol monoether.
To isolate the formal first methylene chloride and un-reacted glycol monoether were separated over a column. The sump of the column consisted of almost pure fo~mal which was subjected to distillation. The pure formal boiled at 102 - 104C under 18 mm of mercury.
E x a m p l e 5 Under the conditions as specified in Example 4, the 37 % formaldehyde solution (81 ~) was added dropwise over a period of ~ hours to the ethylene glycol monomethyl ether to~ether with the catalyst and CX2Cl2, while boiling and separating the water with the aid of the entrainer. In this case the formaldehyde content in the separated water was reduced to 0.4 ~ = 0.01 mole ,~. The yield of formal increased to 96.5 mole % with a selectivity of about 99 mole %, cal-culated on the glycol monoether used.

.

....

HOE 74~ 033 104'7S39 E x a m ~ 1 e 6 ~nder the conditions specified in Exa~mple 1, 600 g of diethylene gl~col monomethyl ether, 30 g of Amberlyst 15 and 1,000 ml of CHC13, corresponding to a proportion by weight to the di~lycol monoether of`2.48 : 1, were heated to boiling temperature and, by means of a piston pump, 303 g of a 25 % formaldehyde solution were uniformly pumped into the mixture over a period of 4 hours. ~he aqueous distillate contained 4.7 g of formaldehyde. ~he conversion of diglycol monoether was 91.7 mole %, the yield after distillation a~ a boiling point of 160C under about 5 mm Hg amounted to 82 mole % of formal of the diglycol monoether~
E x a m p 1 e 7 Under the conditions specified in Example ~, water was removed as an azeotrope wikhin a period of 3 hours from a mixture of 441 g of triethylene glycol monomethyl ether, 74 g of a 58 % formaldehyde solution, 50 g of ~mberlyst~ 5 b~ re-fluxing to~ether with 600 ml of CXC13 (proportion by weigbt to triglycoi monoether 2.03 ~ he temperature in the re-action vessel was 70 - 80C, the discharged water contained 3.8 g = 0.~ mole of formaldehyde. At a conversion of tri-glycol monoether of 75 mole % the formal was obtained, a~ter distillation at 190 - 220C ~mder 3 mm Hg, in a yield of 69.2 mole %, corresponding to a selectivity of 92.2 mole ,~.
Z5 x a m p-l e 8 750 g of a mixture of the followin~ ethers ~rere reacted 27 with 37 % formaldehyde solution in a manner analogous to o~ 74/F 0~3 ~047539 to Example 1:
triethylene glycol monomethyl ether 9.0 ,~ by weigh~
tetra " " " " " 24.2 " " "
penta " " " " " 28.8 " " "
hexa " " " " " 20.8 "
hepta " " " " " 10.8 " '~ "
octa " " " " " 4.7 " " "
higher " " " " ethers 1.7 " " "
~he mixture of the gl~col monoethers was heated to boil at 70 - 80C together with 1,500 g of CHCl3 and 50 g of Amberlyst~15 and during the course of 3 hours 121 g of a ~7 % formaldehyde solution were added dropwise whilst the water was removed with the aid of the entrainer. ~he aqueous distillate contained 3.9 g - 0.13 mole of formaldehyde. ~he catal~st was filtered off and the chloroform was distilled off u~der reduced pressure to~ether with thè residual amount of water and the unreacted formaldehyde. ~he catalyst, the activity of which was unchanged, could be used for further reactions. According to the decrease of the hydroxyl number from 6.9 % to 1.9 % the conversion to the formal of the glycol monoethers was 72.4 %. Unreacted monoethers were distilled off at a sump temperature of up to about 280C.
Coloring matter in the residue was removed b~ adsorption with active carbon or bleaching earth.
E x a m p 1 e 9 In a 0.5 l three-necked flask provided with stirrer, 27 thermometer and a packed column havin~ about 2 - 3 theoreti-~ 47539 HOE 74/F 033 cal plates on which a water separator was mounted for use of an entrainer having a density below 1,76 g = 1 mole of ethy-lene glycol monomethyl ether, 40 g of a 37 ~0 ~ormaldehyde solution, 185 g of isopropyl chloride and 0.38 g of p-tolu-enesulfonic acid, corresponding to 0.5 % by weight, calcu-lated on the glycol monoether, were heated to boiling tempe-rature while stirring. Over a period of 6 hours, 27 g of water were removed with the aid of the entrainer at rising temperature in the flask (38 to 56C). ~he water contained 1.35 g of formaldehyde, corresponding to 9 mole ,' of the amount used, and traces of glycol monoether.
~he yield of glycol monoether formal amounted to 72 13 mole % at a conversion of the glycol monoether of 78 mole %.

~ .,

Claims (8)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for the preparation of an ethylene glycol monomethyl ether formal of the formula [CH3O(CH2CH2O)n]2CH2 wherein n is in the range of from 1 to 8, in which at least one ethylene glycol monomethyl ether is reacted with a 20 to 60% by weight aqueous formaldehyde solution in the presence of an aliphatic chloro- or chlorofluoro-hydrocarbon having a boil-ing point of from 35 to 125°C at atmospheric pressure and in the presence of 0.2 to 20% by weight, calculated on the glycol monoether, of a strong acid having a pK value of less than 4 as catalyst, and the water in the form of an azeotropic mixture is distilled off.

2. A process as claimed in claim 1, in which the aliphatic chlorohydrocarbon is di-, tri- or tetra-chloromethane.

3. A process as claimed in claim 1 in which the strong acid used as catalyst is an ion exchanger of the sulfonic acid type.

4. A process as claimed in claim 1, claim 2 or claim 3 in which the reaction is carried out at a temperature of from 40 to 125°C.

5. A process as claimed in claim 1 in which the aqueous formldehyde solution is continuously added in measured quantitites to a boiling solution of ethylene glycol monomethyl ether in the aliphatic chloro- or chlorofluoro-hydrocarbon containing the strong acid as catalyst.

6. A process as claimed in claim 1, claim 2 or claim 3 in which the proportion by weight of the aliphatic chloro- or chlorofluoro-hydrocarbon to the ethylene glycol monomethyl ether is in the range of from 0.2 : 1 to 5: 1.

7. A process as claimed in claim 1, claim 2 or claim 3 in which the content of formaldehyde in the azeotrope consist-ing essentially of the aliphatic chloro- or chlorofluoro-hydrocarbon and water is reduced by using a rectifying column.

8. A process as claimed in claim 1, claim 2 or claim 3 in which the reaction is carried out at a temperature of from 40 to 125°C with reflux of the aliphatic chloro- or chlorofluor-hydrocarbon or its azeotrope with water.