DE2144304A1 - Process for the production of alpha-hydroxycarboxylic acid, alpha, beta-unsaturated acids and / or their derivatives - Google Patents

Description

Patent Attorneys DIpI.-Ing. R. B Ξ E TZ son.
DIpl-Ιησ. K. LAMPfJSCHT

Dr.-mö. γ ;. D, - .: -njr. 233-17.497P- 3 September I97I

8 M ü η cii 3 η 12, SLeinadorfatr. M.

Vyskumny ustav pre petrochemiu, Noväky (Czechoslovakia)

Process for the production of OC -hydroxycarboxylic acid,

ß-unsaturated acids and / or their derivatives,

The invention relates to a process for the production of OC-hydroxycarboxylic acids, their nitrates, 06, ßunsaturated acids and / or their esters starting from individual olefins or oils by oxidation with nitric acid and / or nitrogen oxides, in particular nitrogen dioxide, in the presence of an inert solvent Temperatures up to 120 ⁰ C and gfs. subsequent dehydration and gfs. Esterification of the corresponding hydroxycarboxylic acids or their derivatives.

It is known that a mixture of oL -Hydroxyisobuttersäurenitrat and OC-hydroxyisobutyric acid is produced by oxidation of isobutylene with a mixture of concentrated or dilute nitric acid and nitrogen dioxide or with pure nitrogen dioxide, by hydrolysis at temperatures of I5 to 150 ⁰ C in the oC -Hydroxylsobutyric acid is converted. The oxidation takes place at temperatures of + 5 ⁰ C and the unused nitrogen oxides are removed under reduced pressure at 25 ⁰ C.

7237) -NÖE (7)

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pulled. By changing the proportion of butylene used and the hydrolysis conditions, the yield changes from 55 mol% (when using 3 mol of dimeric nitrogen dioxide per mole of isobutylene, without nitric acid and water) to 82.7 mol # (with 5.15 mol of nitrogen dioxide, addition of 2 moles of water and continuous increase in the hydrolysis temperature of 4o to 100 ⁰ C). The high excesses of nitrogen dioxide as well as the complicated and ineffective hydrolysis (US Pat. No. 2,847,453) are disadvantageous here.

Isobutylene can be oxidized at temperatures below 50 ^° C. alone with nitric acid or with catalytic amounts of nitrogen dioxide in the presence of copper, vanadium and manganese salts. However, under these conditions only yields of 06-hydroxyisobutyric acid of 40 # are achieved (US Pat. No. 2,877,465).

OC-hydroxyisobutyric acid can be also prepared by reaction of isobutylene with at least 4 moles of nitrogen dioxide (monomer) at temperatures of 0 to 20 ⁰ C, removal of the unused nitrogen oxides by vacuum distillation and hydrolysis with 5 to 20 $ nitric acid at a temperature of 30 ° C ( 0.5 to 3 hours) (U.S. Patent 2,971,981).

The oxidation of isobutylene or propylene is possible even in the presence of other olefins or paraffins, when the gaseous mixture in a mixture of acetic acid and nitric acid in the ratio of 0.5 to 3: 1 is absorbed in the presence of water in amounts up to 15% by weight. . The oxidation temperature is below 100 ° C. The nitrogen dioxide mixed with nitric and acetic acid is fed in countercurrent to the isobutylene solution. The nitric oxide and nitrous oxide produced by the reaction in the presence

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that are formed by water can (before the reaction) be oxidized again to nitrogen dioxide by means of oxygen the. The proportion of nitrogen dioxide should be up to 1 mol (per isobutylene), the yield of (X -hydroxyisobutter acid is about 80 # (U.S. Patent 5,284,494). The technical Implementation requires additional devices, such as mixers for acetic and nitric acid, and extremely large facilities.

In order to limit the formation of by-products, the oxidation of the isobutylene is carried out of the product with water vapor at 100 ° C in the presence of Kalikarbonat and magnesium monoxide with subsequent removal of the excess nitrogen dioxide by blowing air at temperatures of I5 to 5O ⁰ C and the further hydrolysis . (Author's certificate ZSSR 14} 588).

The yields of OC -hydroxylsobutyric acid increase, when the oxidation of isobutylene is carried out with a mixture of nitrogen dioxide and 4o to 56 # nitric acid will. After adding water to the reaction mixture, the excess becomes Nitrogen dioxide is distilled off at atmospheric pressure with a subsequent temperature increase to 85 to 100 ° C. The mixture of nitric and acetic acid that was obtained from the distillation of the hydrolyzate is through Acetic acid regulated in a ratio of 1: 2 (to the advantage of acetic acid). The azeotropic formed during the distillation Mixture is used to regenerate the nitrogen dioxide. (Author's certificate ZSSR 192 779).

These processes require little to obtain maximum yields of 0 * -hydroxycarboxylic acid (or its nitrate).

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at least 6 moles of nitrogen dioxide per mole of isobutylene. There are therefore very large plants for the reaction and processing as well as larger amounts of nitric acid are required.

It is also known that by dehydrating CX -hydroxycarboxylic acids in the presence of polymerization inhibitors in the presence of alkaline or zinc, tin, lead and iron halides *! As dehydration catalysts in the melt, & , β- unsaturated acids are formed (NSR Pat. 1 191 367 and NSR Pat. I 195 295).

The <X -hydroxycarboxylic acids are dehydrated even in the presence of a strong inorganic acid, the salts of strong inorganic acids and of pyridine or a secondary or tertiary alkylamine mixed with the metal halides. (FR-PS 1 106 462; NSR patent 887 040).

According to another process (PR-PS 1 14 13 337) the hydroxy acid is converted into an ester with an organic acid, the boiling point of which is below 180 ° C. The ester is then dehydrated in the presence of the inhibitor and basic catalyst. Similarly, the oi-hydroxy acid in the presence of the basic catalyst in an inert polar solvent (formed by the dehydration of the salts *, / S-unsaturated acid (FR-PS 1,470,913;. NDR Patent OO6 55) The dehydration can also Sulfuric and phosphoric acids can be achieved (US Pat. No. 2,811,545).

A disadvantage of these production processes is the rather low selectivity for the formation of the £ *, ^ -unsaturated Acids as well as the increased consumption of catalyst, which is difficult

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is to be regenerated.

The production processes are multi-level and it is difficult to maintain continuous production.

The methyl ester of (X -hydroxyisobutyric acid can be successfully dehydrated in the presence of a solid catalyst which is produced from acidic sulfates of alkali metals and SiIi- λ cagel (GB-PS 1 04l 702), a mixture of methyl methacrylate and as a reaction product ^ Disadvantages of this procedure are the lower selectivity of the formation of c *, / S -unsaturated acid and its esters and catalyst losses, which are mainly due to dissolution by the water of reaction.

To achieve the tests, the dehydration of 0 (. Hydroxyisobutyric for methacrylic acid with ordinary dehydration catalysts (PPOC * AIPO ,, SiO _2, etc.), no positive results have produced since the Cxi-hydroxyisobutyric it decays to a considerable extent in acetone and the like formic acid (BF Ustavlcikov, MI Farberov, VA Podgornova, Neftechimija 2 (I962) 592.)

With a mixed catalyst consisting of about 70 $ secondary calcium phosphate and J0 # tertiary calcium phosphate (certificate ZSSR 14-589, 152 237) , the dehydration of the ammonium salt of OC -hydroxyisobutyric acid as well as its methyl ester and the free O ^ -hydroxyisobutyric acid can, however can be achieved.

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The dehydration of the methyl ester of OC- hydroxyisobutyric acid with this catalyst in the presence of methanol (author's certificate ZSSR 166 012) produces a mixture of methyl methacrylate and methacrylic acid, the selectivity of methacrylate formation being 84.3 mol # and that of methacrylic acid being 4 mol # . With otherwise very favorable parameters of this catalyst, there is a disadvantage: the rather complicated preparation, which also requires pure starting materials.

The invention now relates to a process for the preparation of C ^ -hydroxycarboxylic acids, their nitrates, o £, ^ »- unsaturated acids and / or their esters from individual olefins or oil mixtures by oxidation with nitric acid and / or nitrogen oxides, especially nitrogen dioxide in the presence of a inert solvent at temperatures up to 120 ° C, which is characterized in that the oxidation is also realized in the presence of the oxide, with the advantage that the excess nitrogen oxides are removed by heating the reaction mixture, by driving them out and / or distilling off Remaining (residue) is possibly added water, preferably in the amount of 5 mol to 1 mol of concentrated olefin, after which the reaction mixture either after hydrolysis at an elevated temperature, preferably at 60 to 80 ° C, or directly by distillation, preferably at a reduced temperature pressure, at the temperature to 150 ⁰ C, preferably to 80 ° C, water, Salpe Separate tertiary acid and lower-boiling organic substances, and the C * -hydroxycarboxylic acid and / or the nitrate in question separates from the distillation residue, or water or steam is fed in during the distillation or in the lower part of the column, preferably in

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the amount of 5 to 15 wt. % On the raw material, the oxidation and the expulsion of nitrogen oxides, the hydrolysis and / or the distillation is preferably carried out in an inert gas stream with the oxygen and / or with air C *, / 2> -unsaturated acids and / or their esters, the crude and / or isolated oC -hydroxycarboxylic acid and / or its ester, or in the presence of the solvent, polymerization inhibitor and stable gas, dehydrated to insoluble or limited in the | Water-soluble phosphates and / or sulfates of the elements II., A III, b IV and VIII. Group, the iron subgroup of the periodic systems, or their mixture, preferably the mixture of secondary and tertiary calcium phosphate, the dehydration of the hydroxycarboxylic acids is preferably simultaneous with their esterification on dehydration and / or dehydration esterification catalysts with the alcohol or with an alcohol mixture in the presence of water in an amount of at least 0.5 $ * preferably 10-2ΟΟ5έ wt. Water, calculated on the hydroxy acid is carried out, or with an inert solvent to give the unsaturated esters and acids separated from the formed raw product in a known manner and the non-% unreacted hydroxy acid and the alcohols are possibly recirculated.

The starting material is formed by (X -olefins, especially isobutylene and propylene, since there is a considerable need for the end products (derivatives of methacrylic and acrylic acid) and these are used on a very broad basis. However, the process according to the invention is also applicable to other olefins applicable, whereby higher Oc , | 3 -unsaturated acids and their derivatives arise.

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Technologies that require pure olefins, this process does not require expensive separation of paraffins, but on the contrary, from the standpoint of heat dissipation, it is their presence even beneficial.

The oxidation reagents (nitric acid, nitrogen dioxide and other nitrogen oxides) can be used individually or in mixtures be used. The nitric acid can also be used in concentrations below $ 100. It is economical very advantageous mixtures of nitrogen oxides used in various technological processes, such as the manufacture from nitric acid or the oxides or from other processes (e.g. oxidation with nitric acid).

The oxidation process takes place in the presence of oxygen, which can be used either pure or mixed with inert gases. It is most beneficial to use air. By introducing oxygen, on the one hand, lower nitrogen oxides and nitrogen oxides present in the starting material are removed on the other hand, lower nitrogen oxides, which are formed in the reaction, are oxidized.

If the oxidation of the olefins is carried out without nitric acid, the oxygen also primarily takes part in the oxidation formed aldehydes to the corresponding acids part, whereby the possibilities of an explosion of the reaction mixture turned off.

The reaction temperature depends on the type of oxidizing agent used. The lowest is that Temperature when using nitrogen oxides (regularly

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-15 to + 10 ⁰ C) j if nitric acid is used alone, one usually works at 40 to 60 ° C

O,

The reaction is carried out either under ordinary or elevated pressure. It can be carried out continuously or in batches. It is important to note the molar ratio of the olefin, particularly to nitrogen dioxide, which will mostly be above 5 moles of oxide per mole of olefin. The nitric acid is usually used in a ratio of 1: to the olefin; larger quantities increase the distillation f tion time, thereby can proceed decomposition processes to a greater extent, in turn.

The excess nitrogen dioxide is removed from the reaction mixture by increasing the temperature. As due to the addition of oxygen to the reaction mixture If lower nitrogen oxides are absent during the reaction, the expelled nitrogen dioxide can immediately be transferred to the Cycle are returned and there are no special oxidation systems for the oxidation of lower oxides necessary.

If you win the OC -hydroxycarboxylic acid or through ™ Cooling off the nitrate of the (X-hydroxycarboxylic acid wants to separate, water is added after the nitrogen dioxide has been removed.

The hydrolysis takes place after the addition of water at increased Temperature, preferably with the simultaneous addition of oxygen or gas containing oxygen. This has the task to oxidize the lower nitrogen oxides resulting from the hydrolysis of the nitrate. The resulting Nitrogen dioxide can be recycled directly to the oxidation of the olefins.

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- ίο -

A very long hydrolysis time at elevated temperature reduces the yield due to the formation of larger 'amounts of By-products. In the case of the oxidation of the olefins with the Nitric acid alone is mainly formed from OC-hydroxycarboxylic acid, albeit in a lower yield, so that the hydrolysis occurs then does not have to be carried out or only has to be carried out for a minimally short period of time.

To achieve maximum yields of acid, it is advantageous to carry out the hydrolysis with simultaneous distilling off Water, nitric acid and lower boiling organic substances. It is beneficial to distillation to be carried out at minimum pressure in order to eliminate the adverse influence of elevated temperatures.

For the same reason as in hydrolysis, it is also advantageous in distillation to use oxygen or oxygen To supply gas. To prevent secondary formation of nitrate as a result of an increase in the concentration of nitric acid in the To prevent "boilers" or the lower part of the column, it is advantageous to use water (preferably in vapor form) in these parts. initiate.

The advantage of the process according to the invention consists in the reduction of the necessary amount of nitrogen dioxide to achieve the same yields of ö £ -hydroxycarboxylic acid, also in the reduction of energy consumption (evaporation of smaller amounts of unreacted nitrogen dioxide and nitric acid, which is either added directly or arises from nitrogen dioxide and water), as well as in the higher performance of the production plants, especially the reactor and the separation plants, furthermore in a reduction

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the amounts of nitrate formed in the digester during the distillation and thus higher selectivity for the formation of Oi-hydroxycarboxylic acids, in particular o ^ -hydroxyisobutyric acid in the case of isobutylene oxidation.

Furthermore, good effectiveness and high selectivity of the dehydration to unsaturated acids and esters, a broader range of easily produced or available catalysts, which on the one hand are sufficiently stable and on the other hand can be easily regenerated, should be mentioned. Your %

Production does not require chemically pure raw materials, rather the other way round. For example, natural, unpurified dolomite can be used to produce the highly effective dehydration catalyst for Oi -hydroxycarboxylic acids, which also reduces production costs. In the case of higher catalyst consumption, a simple replacement for fresh magnesium calcium phosphate or sulfate with admixtures of other sulfates, phosphates, etc., can often be cheaper instead of demanding regeneration, the latter in no way lowering the activity, selectivity or even durability of the catalyst.

The next advantage of the process according to the invention is the single-stage production of the mixture of the ester of the unsaturated acid (eg methyl methacrylate) and the acid (eg methacrylic acid) itself in the claimed composition directly from the (X-hydroxycarboxylic acid and methanol. In comparison to the known dehydration of the According to the invention, esters of hydroxycarboxylic acids - especially due to the action of the added water - the necessary temperature even drops by 100 ^° C. with a simultaneous reduction in the formation of undesirable by-products, such as

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e.g. of acetaldehyde in the dehydration of lactic acid or of acetone in the case of the methyl ester of ot-hydroxylsobutyric acid,

A suitable combination of alcohols and water makes it possible to produce a mixture of the claimed or required composition to get that after extraction e.g. can be easily separated by distillation with dichloroethane. This type is also beneficial because of it is possible with one apparatus and the same catalyst, simply by modifying the type and the ratio the constituents of the solvent, water and alcohol, the ester in the claimed or desired, depending on requirements Win ratio with high yield. Further advantages of the invention emerge from the examples.

example 1

In a 1 l flask with reflux condenser, mixer or stirrer, thermometer and inlet tube for isobutylene, which is immersed in a temperature control bath, 4 mol of nitrogen dioxide and 0.5 mol of 5Q nitric acid are added; 10 minutes before the start of the reaction after the temperature of the reaction mixture has been adjusted to -10 ° C., oxygen is introduced into the mixture in amounts of 1 mol / hour. initiate. Simultaneously with the supply of isobutylene at a rate of about 12 Nl / hour. one begins to measure the reaction time. After addition of 1 mole of isobutylene, the supply of isobutylene and oxygen is stopped, the reaction mixture is heated in 30 minutes to 30 ⁰ C, to the reaction mixture 10 moles of water are added and hydrolysis was begun with heating to 80 ° C within 30 minutes.

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After this temperature has been reached, the mixture is cooled and a mixture is extracted from the flask under reduced pressure (20 torr) subtracted from water and nitric acid; after 500 ml of distillate have been withdrawn, 50 ml of water remain in the flask added and the product distilled off. The distillation

. ο

is finished when the temperature at the top drops to 45 ° C at a temperature of 60 C in the distillation flask. The distillation residue is cooled and filtered. 115 g of product are obtained and 71 g of crystalline product with 95 # (-hydroxyisobutyric acid and 44 g of mother liquor with 70 $ | C * -hydroxyisobutyric acid and 8% nitrate are obtained therefrom. The yield after conversion to C ^ -hydroxylsobutyric acid is 100.7 g to 1.19 moles of isobutylene, ie 81.4 moles #.

In the event that the oxidation takes place in a similar manner, but the yield has been added to the distillation immediately after the addition of water, 80.1 % of hydroxyisobutyric acid is obtained. Under otherwise identical conditions, but without the addition of oxygen, only 70.9 % O ^ -hydroxyisobutyric acid is obtained.

Example 2 ^

In a similar manner as in Example 1 (concentration 56 $) and 3 moles of nitrogen dioxide (dimer) oxygen and isobutylene are introduced at a temperature of about -10 ⁰ C to a mixture of 0.5 mol of nitric acid. After 1.19 mol of isobutylene has been fed in, the reaction mixture is heated to 50 ° C. and, after cooling to 15 ^° C., 180 ml of water are added to the mixture. The mixture is immediately added to the distillation, similar to Example 1, and after crystallization, 60 g of filter cake and 43 g of filtrate are obtained. The business

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stops (χ * -hydroxyisobutyric acid in the crystals is 96.3 $, in the filtrate 69.2 $ in the presence of 10 $ .O (-hydroxyisobutyric acid nitrate. The yield is 73 * 1 $ (after converting the nitrate to O ( -Hydroxyisobutyric acid).

In the event that the reaction takes place under the same conditions but without oxygen, the yield is 77 * 59 S CX -hydroxyisobutyric acid, i.e. 62.7 mol $.

Example 3

The reaction is carried out in the same way as in Example 1, but:
called n-hexane.

carried out, but at a temperature around O ⁰ C with presence

The yield of OC-hydroxyisobutyric acid in the presence of oxygen is $ 76.5, without oxygen is only $ 65.

Example 4

As in Example 1, 8 moles of 56 # nitric acid are placed in the flask. At 6O ⁰ C is introduced into the nitric acid isobutylene in admixture with butanes and oxygen. The further processing is similar to that in Example 1. The cj -hydroxyisobutyric acid is obtained with a yield of $ 65. In the reaction without oxygen, the yield is $ 60.

In the case of the reaction with a mixture of 5.5 mol of nitrogen dioxide (dimer) and 1 mol of nitrogen monoxide The mixture becomes + 10 ° C after the oxidation of the isobutylene

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heated to 20 ° C with oxygen similar to Example 1, 180 ml of water are added to the mixture and the mixture is heated to 80 ° C. At this temperature the hydrolysis takes place for 2 hours. The further processing is similar to that in Example 1. The CX- hydroxyisobutyric acid is obtained in a yield of $ 70, while only $ 58 is obtained without oxygen.

Example 5

In a procedure similar to that in Example 1, 4 moles of a nitrogen dioxide and nitrous oxide mixture are obtained (Ratio 3: 1) 1 mole of propylene at a rate of 8 1 / hour. and air in an amount of J52 1 H. directed.

After completion of the addition of the isobutylene the reaction temperature is allowed to stand still JO minutes under supply of air, and then increases it to 20 ⁰ C. After 3 hrs. The residue is cooled and analyzed. 114 g, ie 85 MoIjC CX -hydroxypropionic acid nitrate, are obtained.

Example 6 d

The dehydration of a 20% by weight aqueous solution of (X- hydroxyisobutyric acid is carried out in a stainless flow-through reactor (internal diameter JO mm; length 500 mm) with a content of 20 ml of dehydration catalyst in tablet form cooled in a water cooler, liquid product is collected in the separator and the gases are passed through a freezing mixture cooled to -20 to -40 ° C. If necessary, non-condensed volatile components are obtained by conducting gas (as

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Carrier gas is used nitrogen with a flow rate of 10 ml / min) through ethylene glycol. Methacrylic acid is found in the product, Acetone and unreacted (X-hydroxylsobutyric acid.

The results of the tests are summarized in Table 1.

Dehydration spray application
rungskatalysa- the solution
gate /. .-1 u- ^
< ^ia cat / ^h ) 0.5 Reaction
temperature
( ⁰ C) conversion
{% Moles) selectivity
in Mol # be
pulled up
Methacryl
acid Calcium ortho- 1.0
0.5 250 78.0 97.0 phosphate 0.9 250
270 45.0
88.0 100.0
96.4 1.6 273 76.4 97.5 0.5 275 56.0 98.7 2.0 300 82.0 95.0 0.5 300 70.0 96.4 2.0 325 83.4 88.9 0.5 325 81.5 96.9 Aluminum phosphate 0.5 274.3 46.8 74.0 1.0 300.0 65.4 66.4 0.5 300.0 40.0 60.5 0.5 325.0 78.6 58.5 0.5 350.0 80.0 50.8 Barium phosphate 1.0 250.0 73.0 92.0 1.0 250.0 47.9 97.5 2.0 300.0 93.0 91.0 300.0 77.0 97.1

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(D (2) (5) (4) (5) Manganese phosphate 0.5 275.0 57.5 95.2 0.5 500.0 84.5 91.1 1.0 500.0 57.5 94.5 2.0 299.0 5'1.5 " 96.5 1.0 525.0 81.4 86.5 2.0 526.8 48.5 92.5 Calcium magnesium 0.5 250.8 62.4 98.1 I. phosphate (from the 0.5 275.0 86.5 95.2 natural Dolo 1.1 274.5 58.5 98.2 with see example 0.5 500.0 82.0 96.8 No. 7) 1.1 500.0 84.9 96.9 1.9 500.0 74.8 97.6 0.5 525.0 82.4 85.5 1.1 525.0 88.0 91.2 1.75 525.0 84.4 95.7 Calcium phosphate 0.5 500 52 80.0 CaJ-F (PO ₁ ^) ,. 1 / 2SiO ₂ 0.5 525 74 69.0 1.0 525 40.7 82.5 2.0 525 25.0 86.5 ^ Calcium sulfate 0.5 225.0 40.5 100 0.5 250.6 68.7 97.5 1.0 250.4 50.5 98.2 0.5 275.0 75.5 96.4 1.0 275.2 60.2 96.5 0.5 500.0 75.0 92.0 1.0 500.0 85.0 95.0 2.0 500.0 65.0 96.0 2.5 500.0 57.0 96.5 2.0 525.0 70.0 94.0

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(D (2) (3) Ul W. 3 (5) 0 Mixture catalyst 52.3 MgO gate; 0.5 275 5 75 2 87 3 14.5 Cr ₂ O ₃ ; 9.65 0 0 1 SiO ₂ ; 16.45 CuO; 1.1 726, 55, 89 4.4 Al ₂ O ₃ ; 1.9 2.1 275 40, 90

CaO and 0.1 ZnO

(However, the service life of the mixed oxide catalyst is short). Example 7

An aqueous solution of 2-hydroxypropionic acid (10% by weight) is dehydrated with a magnesium-calcium catalyst in tablet form with contents of phosphates of other elements, which was prepared from natural dolomite (analysis of dolomite (in %) after annealing : 47.5 MgO; 52.74 CaO; 8.9 Pe ₂ O ₅ ; 0.43 Cr ₂ O ,; 0.0027 SiO ₃ ; 2.98 losses on ignition; 7.5 other carbonates). To the solution of hydroquinone is added in amounts of 0.3 wt.%, Wherein the procedure is similar as in Example 6.

At a temperature of around 300 C and loading of the catalyst with 0.5 1 · ijfa + - * ^h ~ ^ ¹¹ " ^{08 De} i a conversion of

achieved a selectivity of 85 # of acrylic acid.

Example 8

The dehydration of 30 # butyl ester from CX-hydroxy Butyl isobutyrate in butanol is made with magnesium calcium phosphate by a similar procedure as in both

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game 6. At a temperature of 520 ⁰ C and load of the

- 1 - 1
Catalyst from 0.5 1 · 1 «- ,, +. »H can be reached at one

ΙΥαΐ

Conversion of 70 %, a selectivity of $ h% of butyl ester and methacrylic acid, the ratio of butyl methacrylate to methacrylic acid being 25: 1.

Example 9

In a rust-free flow-through reactor (inside diameter 30 mmj length J500 mm) with 20 ml mixture of calcium phosphate | with 15 g of filler is heated to the required temperature, 20 # ^ -Hydroxyisobuttersäurelösung strength (in a mixture of water and methanol in a weight ratio of 1: 1) with 0.1% by weight of hydroquinone as a polymerization inhibitor with a load of 1. 1 Solution / l ... .hours forwarded. The product from the reactor is cooled by a water cooler, the liquid product is collected in the separator and the gases are passed through a freezing agent cooled to -20 to -40 ° C. Uncondensed volatile components are intercepted by gas transport (moderate nitrogen flow of ml / min) through ethylene glycol.

The product contains methyl methacrylate, methacrylic acid, \

CX-hydroxyisobutyric acid and acetone determined. At the specified load and a temperature of 250 ^° C., the conversion of CK-hydroxyisobutyric acid reaches 60 ° and the selectivity of methacrylic acid and methyl methacrylate reaches 30 °, the ratio of methacrylic acid to methyl methacrylate being 4: 1. JOO at ⁰ C, the conversion increased to 70 #, the selectivity remains unchanged, wherein the ratio of methacrylic acid to methyl methacrylate is 1: 1. At 35O ° C a ratio of methyl methacrylate

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lat to methacrylic acid of 3: 1.
Example 10

As in Example 9, 20% C * -hydroxyisobutyric acid solution with 0.1 % inhibitor is passed into the rust-free once-through reactor. In the solvent, the ratio of methanol to water is 3: 1 · With increasing the reaction temperature increases the conversion of 40 $ Mo1 at 250 ⁰ C to 80 mol # at 35O ⁰ C. The burden of the solution is 11. VAS. h " ^1. At 250 ⁰ C is the ratio of methyl

ο
methacrylate to methacrylic acid at 1.5-: 1, at 275 C.

2: 1, at 30O ⁰ C at 3: 1, at 325 ° C at 8: 1 and at
350 ⁰ C at 10: 1 «The selectivity of methacrylic acid and
Methyl methacrylate is up to 325 ° C over 90 mol £, at 350 ⁰ C at 80

Example 11

In the stainless steel flow reactor as in Example 9, a 20 # solution of CX-hydroxyisobutyric acid and
0.05 # inhibitor (the solvent is formed by a mixture of methanol and water in a ratio of 7: 1)

-1 -1
at a speed of 1 1. I ₁ ,., +. . h, at one

Λα.I /.

Temperature of about 325 C. The conversion achieved 73 to 80 # and the selectivity of methacrylic acid and metha crylate 90 $, the ratio of methyl methacrylate to Methacrylic acid is 16: 1.

Example 12

In the stainless steel flow reactor as in Example 9 a solution of (X-hydroxyisobutyric acid (conc. 20 $)

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in methanol and water (as a solvent; ratio of methanol to water of 20: 1). At one temperature of 325 ° C is a conversion of the hydroxyisobutyric acid of 70 mol # reached, the selectivity of methacrylic acid and methacrylate reached 90 MoIJi. The ratio of methacrylate to methacrylic acid is 25: 1.

Example 13

In the reactor with the catalyst as in Example 9 I, at a temperature of 250 ^° C., a 20 # strength solution of 0 ( -hydroxyisobutyric acid in a mixture of methanol and water as a solvent at a load of 0.25 1 ¹ · ⁿ " initiated. When changing the ratio

from methanol to water from 1 ·! 0, T: 1, 3! 1, 1: 1, 1: 2, and 0: 1 the conversion increases from 50 mol $ in the reaction in neat methanol, over 70 mol $, in the ratio 3: 1, to 90 mol;, with pure water, with a selectivity of 92 to 98 mol #. The ratio of methyl methacrylate to methacrylic acid drops from 50: 1 (when reacting with pure methanol) to 1: 1 (when reacting with methanol to water of 1: 2).

Example 14

A 50 # strength solution of O'-hydroxyisobutyric acid in n-butanol and water with a weight ratio of butanol to water of 3: 1 is passed into the reactor as in Example 9. At a load of 0.5 1 C _at b ~ and a temperature of 275 ° C with a conversion of 80 mol #, a selectivity of butyl methacrylate and methacrylic acid of 92 mol # is achieved. The ratio of butyl methacrylate to methacrylic acid

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acidity is 10: 1. Example 15

^{A 30 # strength solution of Oc 1} -hydroxyisobutyric acid is passed into the rust-free once-through reactor as in Example 9. A mixture of methanol and butanol in a ratio of 2: 1 is used as the solvent. At 500 C and a load of the catalyst of 0.5 1 · ijcat ^{'h "we i} a conversion of 70 $ reached ^<a selectivity of 9OJi, wherein the ratio of methyl methacrylate to butyl methacrylate and methacrylic acid 25: 4: accounts. 1

Example 16

The dehydration and simultaneous esterification of a 20% solution of O ( -hydroxyisobutyric acid with the addition of 0.1% polymerization inhibitor was carried out in the rustproof continuous reactor with 20 ml of catalyst. A mixture of methanol and water in a ratio of 3: 1 was used as the solvent. Various dehydration catalysts were tested at 275 ° C. and a load of 0.5 1 t 11 hours, namely: calcium, barium, manganese, magnesium, iron, strontium phosphate and aluminum phosphate, as well as calcium sulfate, barium sulfate and a mixed oxide catalyst

Sator made of 52.3 # MgO, 9.65 # SiO ₂ ,

CuO and 1.9 # CaO. The conversion under the specified Conditions reached 60 to 95 # with a selectivity of 80 to 99 #, the molar ratio of methacrylate to methacrylic acid being 10 to 15: 1.

Example 17

In the reactor as in Example 9, a 209811/1883

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Solution of Ctf-hydroxyisobutyric acid in a solvent of methanol, acetone and water in a ratio of 5: 1: 1. With a load of 0.5 1. 1 ^ ₊ . . dog

IVcL U

a reaction temperature of 275 C, a selectivity of $ 93 was achieved with a conversion of 80 # The ratio of methacrylate to methacrylic acid was 15: 1.

Example l8

A 65 # strength solution of CX -hydroxyisobutyric acid in acetone is passed into the reactor as in Example 9, 2-ethylhexanol and methanol (co-flowing) being added to the mixture. The ratio of alcohols in the acid solution is 2: 1, the ratio of 2-ethylhexanol to methanol being 1: 1. With a load of 0.5 1. * Kat * ^h ~ ¹ ^ ^a temperature of 270 ⁰ C erKat
a conversion of 85 mol # and a selectivity of 905ε is sufficient. The product contains Meth: ^r lwethacrylat, 2-ethylhexyl methacrylate · * and methacrylic acid in a ratio of 15: 3: 1 ·

Example 19

In the filled with 20 ml calcium magnesium phosphate d

Continuous reactor is according to the procedure as in Example 9 a 30 # solution of lactic acid with 0.5Si hydroquinone passed. A mixture of methanol and water in a ratio of 3: 1 is used as the solvent. At 350 ° C and

-1 -1 a loading of the catalyst of 0.5 1 · ^ v _& ^ · ⁿ , a selectivity of acid and methacrylate of 80 # is achieved in the conversion, the ratio of methacrylate to acrylic acid being 5: 1.

209811/1883

Claims (1)

- 24 claim Process for the preparation of CX -hydroxycarboxylic acids, their nitrates, O <" _} {*> -unsaturated acids and / or their esters starting from individual olefins or olefin mixtures by oxidation with nitric acid and / or nitrogen oxides, in particular nitrogen dioxide, in the presence of an inert solvent Temperatures up to 120 ⁰ C, thereby w characterized that the oxidation takes place in the presence of oxygen (the oxide), the excess nitrogen oxides are expelled or distilled off by heating the reaction mixture, gfs to the remainder. Water, preferably in an amount of 5 mol per 1 mol of concentrated olefin, is added, after which from the reaction mixture either after hydrolysis at an elevated temperature of preferably 6o to 80 ° C or immediately water, nitric acid and lower-boiling organic substances, preferably at reduced pressure at a Temperature up to 150 ⁰ C, preferably up to 80 ⁰ C, distilled off and the Of-hydroxycarboxylic acid and / or the corresponding from the distillation residue be separated α nitrate or it is fed in the distillation or in the lower part of the column, water or steam, preferably in an amount of 5 to 15 wt.% (based on the raw material), the oxidation and the expulsion of the nitrogen oxides, the hydrolysis and / or the distillation is preferably carried out in an inert gas stream with oxygen and / or with air, after which gfs. the crude and / or isolated Ο ** - hydroxycarboxylic acid and / or its ester for the production of W, ^> -unsaturated acids and / or their esters, in particular in the presence of a solvent, polymerization inhibitor and carrier gas in the presence of insoluble or limited water solubility Phosphates and / or sulfa 2 0 9 8 11/18 8 3 th of elements of the II., a III., b IV. and VIII. group (iron subgroup) of the periodic table or their mixtures, preferably a mixture of secondary and tertiary calcium phosphate, is dehydrated, preferably at the same time as their esterification (in the presence of ^ of dehydration / or dehydration esterification and) with alcohol or an alcohol mixture in the presence of water in an amount at least 0.5 $ j pre preferably 10 to 200 wt.% (based on the hydroxycarboxylic "acid) and gfs. in an inert solvent, the unsaturated esters and acids being separated off in a known manner from the crude product formed and the unreacted hydroxycarboxylic acids and alcohols being recirculated if necessary. 20S811 / 1883