CA1198429A - Catalysis of condensation reactions - Google Patents

Abstract

ABSTRACT
Certain hydrogen phosphate and pyrophosphate compositions are employed as catalysts for organic condensation reactions. Particularly high conversions and selectivities are obtained by the use of synergistic mixtures of in cyclization reactions such as in the conversion of hydroxyethylpiperazine to triethylene-diamine and morpholine to dimethylaminoethylmorpholine.

Description

~9~ ~9 CATALYSIS OF CONDENSATION REACTIONS

This application is a division of copending Canadian Patent Application No. 405,618, filed June 21, 1982, and is also related to copending Canadian Patent Application No.
400,220, filed March 31, lg82.
TECH~ICAL FIEI,D OF THE INYENTION
The present invention relates to organic condensation reactions effected in the presence oi novel pyrophosphate and hydrogen phosphate catalysts and is more particularly concerned with the production of amine compounds in enhanced yields.
BACKGROUND OF THR PRIOR ART
-Organic synthesis by condensation reactions resulting in the loss of a molecule of water or of ammonia are well known in the art. Certain of such reactions are generally effected in the presence of acidic catalysts. An important area in which such acid catalysis has been employed is in cycliæation reactions as in the synthesis of triethylenediamine and its C-substituted homologues. The catalysts more generally

2~ used or proposed for use in such cyclization reactions are solid products of the Lewis acid type.
Triethylenediamine, also called diazabicyclo -[2.2.2]-octane, has been widely employed commercially as a catalyst in organic isocyanate reactions with compounds containing labile hydrogen, as in the production of urethane polymers.
Triethylenediamine (sometimes hereinafter referred to as TEDA) was initially prepared 119~i29 in significant q~lantities by methods such as that described in U.S. Patent No. 2,937,176, by passing aliphatic amines in vapor phase over acidic cracking catalyst, such as silica-alumina dried gel or acid activated clays. Numerous other feed stocks as well as other catalysts are disclosed in subsequent patents for preparation ~f TEDA as well as C-alkyl derivatives thereof.
Typical among these are U.S. Patents 2,985,658 and

3,166,558 employing preferably silica-alumina type catalyst, but listing also other useful solid acid catalysts that can be employed such as alumina in which phosphate or fluoride ion is incorporated (U.s. 2,985,658~.
Among other catalysts proposed in the patent art for preparation of triethylene diamine and/or C-alkyl homologues there~f, are certain phosphate compounds, particularly aluminum phosphate.
The use of aluminum phosphate as a catalyst in the preparation of heterocyclic compounds from aliphatic amines was early disclosed in U.S. Patent 2,467,205, particularly for the preparation of piperazine from ethylenediamine or from polyethylene polyamine. The use of aluminum phosphate as catalyst in the preparation of triethylenediamine accompanied by piperazine among other by-products is further described in U.S. ~atent 3,172,891; while U.S. Patent 3,342,820 describes the use of complex phosphates of alkali metal and trivalent metals in the preparation of C-alkyl TEDA.
U.S. Patent 3,297,701 discloses as catalysts for preparation of TEDA and C-alkyl TEDA, in addition to the preferred aluminum phosphate stated to be superior, other phosphate compounds including calcium and iron phosphates among other listed metal phosphates. In the conversion of N-aminoethylpiperazine to triethylenedi-amine over aluminum phosphate catalyst, at most up to39 mol% triethylenediamine is said to be obtained.
Other of the named metal phosphate catalysts in the ~iL98~2~
examples of the patent obtain yieids of less than 10 mol% TEDA.
Acid metal phosphate catalysts, particularly phosphates of boron, aluminum and trivalent iron, have also been proposed for use in intramolecular cyclic dehydration reactions and other condensation reactions involving amino compounds. Examples of such reactions are found in U.S. Patent

4,117,227, which discloses conversion of an N-substituted diethanolamine to the corresponding N-substituted morpholine. U.S. Patent 4,036,881 describes preparation of non-cyclic polyalkylene polyamines by condensation of an alkylene diamine with an ethanolamine. N-hydroxethylmorpholine is condensed with morpholine in the presence of aluminum phosphate catalyst to form dimorpholino ethane according to U.S. Patent 4,103,087. Similarly, dimorpholinodiethyl ether is obtained by condensation of hydroxyethyl morpholine with aminoethyl morpholine over iron, aluminum or boron phosphate in U.S. Patent 4,0g5,022. Reaction of piperazine with ethanolamine over such acidic metal phosphate pro~duces N-aminoethyl pipera~ine according to U.S. Patent 4,049,657. V.K. Patent 1,492,359 discloses the preparation of morpholine compounds by reacting an aminoalkoxyal~anol compound over phosphoric acid and similar types of phosphorus-containing substances.
Pyrophosphates of lithium, sodium, strontium and barium have been used as dehydration catalysts; see U.S. Patent 3,957,900. Phosphates and pyrophosphates of strontium and nickel have been used for the dehydrogenation of, for example, n-butene to butadiene under the conditions described in U.S. Patent 3,541,172.
SUMMARY OF THE INVENTION
In its broadest aspect the present application, a division of copending Canadian Application No. 405,618, filed June 21, 1982, is concerned with the provision in methods for the synthesis of organic compounds by condensation reactions in the presence of phosphate catalysts, by the improvement which comprises the use as such of catalysts which are selected from the group consisting of the pyrophosphate and dihydrogen ~' ~ 4 ~ 11984Z9 phosphate of strontium, and mix~ures thereof, together with mixtures of at least one of the pyrophosphate and dihydrogen phosphate of strontium with the monohydrogen phosphate of strontium.
DETAILED DESC~IPT~O~ OF ~E INVEN~ION
The monohydrogen and dihydrogen phosphate catalysts of the present invention are prepared by reaction of a mono- or diphosphate of an alkali metal or a~monium with a soluble salt of strontium, copper, magnesium, calcium, barium, zinc, aluminium, lanthanum, cobalt, nickel, cerium or neodymium at ambient temperatures. The highest purity and best yields of the present invention are obtained when using the soluble metal salts of a strong acid such as the metal nitrates, in substantially stoichiometric proportion to the phosphate. In aqueous media under these conditions, the reaction mixture is at a pH of about 3.5 to 6.5.
In general, to obtain a precipitate of desired high content of the metal monohydrogen or dihydrogen phosphate~ the ratio of phosphate to metal salt in the reaction mixture should be such as to have a pH of 5 ~ 3, or the mixture should be adjusted to that pH range.
The pyrophosphate form of the catalysts of the present invention are prepared by heat treating the metal monohydrogen or dihydrogen phosphate product at temperatures above about 300C up to 750C in the presence of a mixture of steam and air, preferably at least about 20% by volume of steam.
For use as a catalyst, the metal pyro-, monohydrogen or dihydrogen phosphate product may be employed in the form of irregular particles of the desired size range prepared by breaking up the washed and dried filter cakè or in the form of regular shaped pellets obtained by known methods of casting or extruding or the product ~'..`' 8~i~9 may be deposited or otherwise impregnated into the pores of a microporous substrate such as alumina, silica, silica-alumina, and the like. In using the catalyst of the present invention to catalyze organic condensation reactions, substantially the same condi-tions may be employed as when using the ~nown catalysts for the particular synthesis. For optimum results, however, some adjustment in temperature, diluent and/or spac~
rate may be ound beneficial.
Some specific examples of the type of organic compounds selectively obtained by the method of this invention include T~DA, the aliphatic alkylamines such as methylamine, methylethylamine, dimethylethylamine, morpholine, and dimethylaminoethylmorpholine. In the production of these compounds, the temperature is in the range of about 285 to 420~C, the pressure is in the range of about G.1 to 1.5 atmospheres, and the liquid hourly space velocity (LHSV) of the organic feed stock per ~olume of catalyst is in the range of about 0.05 to 1.5. Preferably depending on the particular reaction, the temperature is in the range of about 300 to 400~C, the pressure is in the range of about 0.3 to 1.O atmospheres and the LHSV is in the range of about 0.1 to 0.3 to obtain the highest yields and most econom-~5 ical process. The operable ratio of the organic feedsto water diluent is about 10 to 90% on a weight basis and preferably, 20 to 80% by weight. The optimum yield of these compounds is likely to be obtained using the highest temperature in the preferred range at the lowest LHSV.
In the preparation of TEDA, the preferred catalyst is selected from the group consisting of monohydrogen phosphate of calcium, magnesium, zinc, mixtures of strontium and ~arium in the ratio of Sr to Ba o about 1 to 5 to 5 to 1 and mixtures of lanthanum and strontium in the ratio of La to Sr of about 15 to 1 to 15. The organic feed stock used in this reaction to produce 119~4Z~

TEDA is a substituted piperazine compound selected from the group consisting of hydroxyethylpiperazine and aminoethylpiperazine. The catalysts of this invention are relatively uneffected by the purity of the feed stock. For example, high conversion and go~d yields can be obtained from crude hydroxyethylpiperazine which contains minor quantities of piperazine and bis hydroxy-ethylpiperazine.
In the preparation of dimethylaminoethylmorpholine (DMAEM), the preferred catalyst is a mixture of strontium and nickel monohydrogen phosphate in the ratio of Sr to Ni of about 1 to 5 to 5 to 1. The feed stock is morpholine and dimethylethanolamine in the molar ratio in the range of about 1 to 3 and 3 to 1. Preferably, the reaction takes place in the presence of hydrogen in the molar ratio of hydrogen to organic feed of about 1 to 1 to 20 to 1 and an inert gas such as nitrogen, argon or helium in the molar ratio of inert gas to organic feed of about 1 to 1 to 20 to 1.
In the preparation of morpholine co~pounds, e.g.
morpholine and alkyl morpholine, wherein the alkyl group has from 1 to 6 carbon atoms, diglycolamine compounds, e.g. diglycolamine and alkyl diglycolamines, wherein the alkyl group has from 1 to 6 carbon atoms are preferably carried out in the presence of strontium monohydrogen phosphate at about 300 to 370C with the other conditions remaining the same as that discussed above. ~his reaction also preferably takes place in the presence of the inert gas in ratios of 2 to 1 to 10 to 1 inert gas to liquid organic feed stock.
The methods and catalysts of this invention are also capable of reacting an alcohol and a nitrogen-containing compound selected from the group consisting of ammonia, aliphatic primary and secondary amines, and aromatîc primary and secondary amines to selectively con~ert this compound to the corresponding symmetrical or unsymmetrical higher molecular weight amine with 1~l91~'~29 little, if any, conversion to the correspondinq ~y-products of thermodynamic amine equilibration. The amines and alcohol in the feed stock each contain 1 to 20 carbons per molecule~
Preferably, the catalyst is lanthanum or copper monohydrogen phosphate and the molar ratio of alcohol to nitrogen-containing compound ranges from about 1 to 6 to 6 to 1.

CATALYST PREPARATION
Example 1 200 grams of strontium nitrate [Sr(NO3)2] was dissolved in distilled water and brought to a total volume of 800 cc with distilled water. To this solution there was added 10 cc of 8S%
phosphoric acid followed by 34.5 cc of 50% sodium hydroxide added rapidly with vigorous stirring. The resultant fine white precipitate was stirred for 10 minutes, vacuum-filtered and water-washed. The obtained filter caXe was air dried in a static oven at approximately 110C and extruded into 1/8 inch pellets for evaluation.
The obtained product had a surface area of 10-15 m /g.
By X-ray diffraction the principal component was identified as ~-SrHPO4 with minor quantities of Sr5(OH~ (PO4)3 and unreacted Sr(NO3~2. Infrared spectroscopy showed a spectrum consistent with SrHPO4. SRef: Richard A. Nygurst and Ronald O. Kagel, "Infrared spectra of Inorganic Compounds", page 163, 1971).

Example 2 212 grams of Sr(NO3)2 were dissolved in distilled water and diluted to 500 cc. 115 grams of ammonium dihydrogen phosphate --NH4H2PO4-- were dissolved in distilled water and diluted to 500 cc. The salt solutions were then combined with heat and stirrPd. The combined solution was vacuum filtered and the resulting precipitate was washed with distilled water and air dried overnight in a static oven at approximately 110 C. The resulting catalyst was believed to contain less than 5 strontium dihydrogen phosphate --Sr(H2PO4)2-- with the balance 8 ~1~8~9 being SrHPO4. The surface pH of this catalyst mixture was 4-4.6 in comparison to substantially pure strontium monohydrogen phosphate which has a surface pH of 4.8-5.4.
Substantially pure strontium dihydrogen phosphate was found to have a surface pH of 0.2-1.2; see Example 5.
The product of this example was deposited on silica-alumina spheres by placing the amount of catalyst to be coated into a jar with Alundum spheres and rotating on a jar-mill for several days to cause the catalyst powder to adhere to the spheres.

Example 3 A catalyst preparation procedure was employed in which 212 grams of Sr(NO3)2 was dissolved in distilled water and thereafter diluted with distilled water. Di basic ammonium phosphate was also dissolved in distilled water and diluted with distilled water with heat. The salt solutions were then combined with heat and stirre~d. The combined solution was vacuum filtered and the resulting precipitate was washed with distilled water and air dried overnight in a static oven at approximately llO~C. The resulting strontium monohydrogen phosphate catalyst had a surface pH o~ 4.8-5.2.

~9~4~
g Control s 1- 3 The followin~ salts were also combined in the manner ~f the Exampl e 1 pr epa rat i o n .

Catalyst Control Salt Solutions Formulatior (a) (b) 261g. Ba (N03)2 :BaS04 2 75g . CsCl40g . (NH4) 2HP04 CsHP04*
3 106g. Sr(N03)40g. SO% NaOH~ . SrHAsO4 2 80e (~H4)2H2A54 *Did not fonn a precipitate.

lo 119~3 ~Z9 Control 4 200 grams of Sr(NO3)2 were dissolved in distilled water and diluted to 400 cc. 92 grams of H2SO4 were diluted in 200 cc. of distilled H2O. 75 grams of 50 wt. % NaOH solution were diluted to 200cc. with distilled water. The H2SO4 and NaOH
solutions were mixed together slowly. The Sr~NO3)2 solution was stirred into the solution containing H2SO4 and NaOH. The solution was stirred for 10 minutes and the precipitate was filtered, washed and dried. The surface pH of the resulting catalyst was less than 3 which was believed to be substantially all SrSO4.

Example 4 The SrHPO4 catalyst of Example 3 was heat treated for 2 hours in the presence of a mixture 20% by volume steam and the balance air at 350C. The resulting strontium pyrophosphate tSr2P2O7) had a crushing strength of 0.47 kg./mm of length and a packed bulk density of 1.01 kg./l.

Example 5 132.5 grams of strontium hydroxide octahydrate --Sr(OH)2.8H2O-- were dissolved in a solution of 750 cc. of 85~
phosphoric acid and 1500 cc. of distilled water. The resulting solution was slowly evaporated to a total volume of about 900 cc.

4~

with the temperature being maintained at 25 to 30Co The solution was cooled to 5C overnight and a white precipitate was recovered by vacuum filtration. The resulting Sr(H2PO4)2 precipitate was washed with 5-300cc. portions of anhydrous ethanol and with 2-200 cc. portions of anhydrous ether. The product was dried at room termperature under vacuum for 6 hours~ An elemental analysis of the product showed a P/Sr mol ratio of 2.04 and the surface pH was found to be ~.2-1.2. The fine powder was pressed into tablets the size of a typical "Aspirin" (registered trade mark) tablet and crushed to granules 1/8 to 1/4 inch in size.

Example 6 The fine powder of the catalyst prepared in accordance with Example 5 was deposited on silica-alumina spheres in the manner set forth in Example 2.

Example 7 2000 grams of Sr(NO3)2 were dissolved in 2000 cc of deionized water and the solution diluted to 4000 cc with deionized water after dissolution of the Sr(NO3)2 was complete.
In another container, 1342.3 grams of Na2HPO4 were dissolved in 2000 cc of deionized water. After solution of the Na2HPO4 was complete, the solutions was diluted to 4000 cc with deionized water. The pH of this solution was approximately 8.8.
Precipitation of SrHPO4 was effected by slowly adding the Na2HPO4 solution to the Sr(NO3)2 solution with rapid stirring.
The white SrHPO4 precipitated rapidly from solution forming a rather thick slurry. This slurry was mixed for one hour, after which time the pH was measured to be about six.
The solid SrHPO4 was recovered by filtering on an eight frame filter press using cloth filters. It was washed with deionized water. After filtering and washing, the solid was dried in a circulating hot air oven at 250F for four hours.

12 ~ ~ 9~42~
The yield of SrHPO4 was 1680 grams. The solid was wetted and formed into pellets by extrusion through a 3.1 mm die plate and cutting the extrudates to about l/4 inch in length. After drying the extrudate at 250F for four Hours in a circulating hot air oven, they were heat treated at 662F for two hours in a 20~ steam, 80~ air atmosphere.

USE OF CATALYST_ Examples 8-15 Several of the products prepared in accordance with the above Examples and Controls l and 3-5 above were evaluated for catalytic performance for the preparation of TEDA with either a feed mixture containing hydroxyethylpiperazine (HEP) or N-aminoethylpiperazine (AEP) in accordance with the following test procedure:

(a) 20 cc (approximately 6.2g.) of the catalyst was loaded into a 3/4" diameter stainless steel reactor.
(b) The reactor was placed in a conventional tube furnace such that the catalyst bed was near the furnace center and therefore could be heated to a constant and uniform temperature.
(c) The catalyst bed termperature was raised to a termperature of 340- 400C over a period of 15 to 30 minutes while a small flow of gaseous nitrogen was maintained through the reactor to àid in the removal of water vapor.
(d) A feed mixture containing HEP and water such that the organic component made up 60% of the mixture was than allowed to flow through the catalyst bed at a rate of 6.5-7.0 cc/hour; the nitrogen flow was discontinued.
(e) The catalyst bed temperature indicated in the tables set forth below was maintained during the run and the product samples were collected and analyzed.

I~,r ~ , 2g Analyses were performed using well-established gas chromatographic techniques.
The yields of TEDA and piperazine (PIP) as well as the conversion obtained from the catalysts within the present invention of the above Examples in Table 1 can be compared with those of Control Catalysts l and 3-5 in Table 2 below.

~ 9~4Z9 ~ P~ ~ ~ ~ ~ P.
C) v o o o C~ o o o . o o <~ o ~ ~ 5 E~ r7 ~ ~: ~ o ;?~ .

~ O O
~ C) ~ . ~ ~ ~ o ~ ~

H ~ d~
r-~ E-~ a~ ,.
1~ ~ 3 ~1 E~ ~ r~ o ~ o a~
a) u~ ~ O ~ ~ ~ ~ o E~'~ ' ' a~

N N
~1 1 ~ d~ d~

~: ~' ~d' ~d~ t~ t`r N N N N
I o ~ N ~ h U~
.
Q> a V ~ V ~
~ ~ @ ~ ~ S ~ S

) V N U~ N U~
Lr~ R~ I
C~ U~ r~ r ~0 X
N r.~J
V
~ P o ~ r.
X ~ a) ~ ~ ~ ~ ~ ~ r~
~ ~ _ .

~ W ~ ~ ~ ~ ~
V

o o o o o U) ~ ~ O O ~`
F ~ r~
E~

~ ~ ~ 3 3 .
O ~ ~ ~ ~ ~D 0.
~-~ O ~ ~ ~ ~ o a o U~ ~ ~
v ,~
3 ~ o o ~
` t`
~ O~ ~ ~D ~ O t` r~
P~ aJ , . . . . . ~ ~
~-r~ ~ ~D ~t-- ~ ~D C`J -r~
~: ~ ,, 3 ~ ~
~ ~,q a a~ . . . . ~
~.,1 d~ ~ ~~ a~ ~ ~
E~ ~ ~ ~ ~ ~ o o I h' C) O O ~ P~
o rd d' Il)tQ
O ~ ~1 O ~ ~¢O O O 0 1~
:Z (~ h h h ~ P~ X X
U~
O O
h h ~a ~ ~ ~
U~ ~ ~U~ U~ U~ ~ ~
h -( O OOO ~ ~ r-l ~ ~:
O :~ ~) h~) h ~ ~ ,C ~ ,~ 0 0 h u~ ~ U) ~ h h S~ ,q .q e~ ~ o o +~
4~ ~ 0 0 O _ _ ~, u~ ~ I`
O _.
d ~
~>

U

34~9 The results set forth in Table 1 where the catalysts of the examples demonstrate a unique ability to convert significant amounts of the feed to products the majority of which is TEDA.

~,

Claims (28)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In a method for the synthesis of organic amine compound by a condensation reaction of an amine in the presence of phosphate catalysts, the improvement which comprises using as the catalyst a member selected from the group consisting of the pyrophosphate and dihydrogen phosphate of strontium, and mixtures thereof, together with mixtures of at least one of the phyrophosphate and dihydrogen phosphate of strontium with the monohydrogen phosphate of strontium.

2. The method as defined in Claim 1 wherein said catalyst is associated with a carrier of the group consisting of silica, alumina and silica-alumina.

3. A method for the synthesis of an organic amine by reacting an alcohol with an amine or ammonia in the presence of phosphate catalysts, the improvement for enhanced activity and selectivity which comprises using as the catalyst a member selected from the group consisting of the pyrophosphate and dihydrogen phosphate of strontium, and mixtures thereof, together with mixtures of at least one of the pyrophosphate and dihydrogen phosphate of strontium with the monohydrogen phosphate of strontium.

4. The method as defined in Claim 3 wherein said catalyst is associated with a carrier of the group consisting of silica, alumina and silica-alumina.

5. The method as defined in Claim 1, wherein the amine is subjected to said condensation reaction resulting in the elimination of water.

6. The method as defined in Claim 1, wherein the amine is subjected to a condensation reaction resulting in the elimination of ammonia.

7. The method as defined in Claim 1 or 2, wherein said amine is cyclized by said condensation reaction.

8. The method as defined in Claim 1, wherein hydroxyethylpiperazine is subjected to condensation to form triethylene-diamine.

9. The method as defined in Claim 1, wherein crude hydroxyethylpiperazine is subjected to a condensation reaction to form triethylenediamine.

10. The method as defined in Claim 1, wherein ethanolamine is subjected to a condensation reaction to form triethylenediamine.

11. The method as defined in Claim 1, wherein N-aminoethylpiperazine is subjected to a condensation reaction to form triethylene-diamine.

12. The method as defined in Claim wherein said condensation reaction comprises reacting an alcohol and an amine or ammonia in the presence of said catalyst to form an aliphatic or aromatic amine.

13. The method as defined in Claim 1 or 2, wherein the reaction is carried out in the presence of an inert gas.

14. The method as defined in Claim 8, 9, or 10, wherein the reaction is carried out in the presence of water.

15. A method which comprises converting a substituted piperazine compound selected from the group consisting of hydroxyethylpiperazine and aminoethylpiperazine to triethylene-diamine at a temperature in the range of about 285°C to 420°C, a liquid hourly space velocity of about 0.05 to 1.5 in the presence of a catalyst selected from the group consisting of the pyrophosphate and dihydrogen phosphate of strontium with the monohydrogen phosphate of strontium.

16. A method which comprises converting hydroxyethylpiperazine to greater than 50 mol. % yield of triethylenediamine at a temperature in the range of about 340°C to 400°C, a liquid hourly space velocity of about 0.1 to 0.3 in the presence of a catalyst selected from the group consisting of the pyrophosphate and dihydrogen phosphate of strontium, and mixtures thereof, together with mixtures of at least one of the pyrophosphate and dihydrogen phosphate of strontium with the monohydrogen phosphate of strontium.

17. A method which comprises converting morpholine and dimethylethanolamine to dimethylaminoelthylmorpholine in the presence of water and hydrogen at a temperature in the range of about 285°C to 420°C, a liquid hourly space velocity of about 0.05 to 1.5 in the presence of a catalyst selected from the group consisting of the pyrophosphate and dihydrogen phosphate of strontium, and mixtures thereof, together with mixtures of at least one of the pyrophosphate and dihydrogen phosphate of strontium with the monohydrogen phosphate of strontium.

18. The method as defined in Claim 17, wherein an inert gas is present during the conversion.

19. A method which comprises covering a diglycolamine compound to a morpholine compound at a temperature in the range of about 285°C to 420°C, a liquid hourly space velocity of about 0.05 to 1.5 in the presence of a catalyst selected from the group consisting of the pyrophosphate and dihydrogen phosphate of strontium, and mixtures thereof, together with mixtures of at least one of the pyrophospate and dihydrogen phosphate of strontium with the monohydrogen phosphate of strontium.

20. The method of Claim 19, wherein the conversion takes place in the presence of an inert gas.

21. The method of Claim 19, wherein said diglycolamine compound is selected from the group consisting of diglycolamine and alkyl diglycolamine and mixtures thereof and said morpholine compound is selected from the group consisting of morpholine and alkyl morpholine and mixtures thereof, wherein each of said alkyl groups contains from 1 to 6 carbon atoms.

22. A method which comprises converting diglycolamine to morpholine at a temperature in the range of about 285°C to 420°C, a liquid hourly space velocity of about 0.05 to 1.5 in the presence of a catalyst selected from the group consisting of the pyrophosphate and dihydrogen phosphate of strontium, and mixtures thereof, together with mixtures of at least one of the pyrophosphate and dihydrogen phosphate of strontium with monohydrogen phosphate of strontium with the monohydrogen phosphate of strontium.

23. The method as defined in Claim 22, wherein the conversion is carried out in the presence of water.

24. The method as defined in Claim 22 or 23 wherein the conversion takes place in the presence of an inert gas.

25. The method as defined in Claim 12, wherein the amine is selected from the group consisting of primary and secondary aliphatic and aromatic amines having from 1 to 20 carbon atoms per molecule.

26. The method as defined in claim 1, 2 or 3 wherein the catalyst comprises strontium dihydrogen phosphate.

27. The method as defined in claim 4, 5 or 6, wherein the catalyst comprises strontium dihydrogen phosphate.

28. The method as defined in claim 12 or 25, wherein the catalyst comprises strontium dihydrogen phosphate.