Cured compositions of epoxy resins with 2,6-diketo-N-carboxymethylmorpholine
United States Patent rm Hindersinn et al.  
  1*Apr. 29, 1975 CURED COMPOSITIONS OF EPOXY RESINS WITH 2,6-DlKETO-N-CARBOXYMETHYLMOR- PHOLINE {75] Inventors: Raymond R. Hindersinn. Lewiston;  
 George C. Hopkins, Clarence; Charles S. llardo, Tonawanda, all of NY.  
 [73] Assignee: Hooker Chemicals &amp; Plastics Corporation, Niagara Falls, NY.  
 [ Notice: The portion of the term of this patent subsequent to Sept. 5, l98), has been disclaimed.  
 (22] Filed: July 24, 1972 1211 Appl. No: 274,715  
  Related U.S. Application Data [60] Continuation-impart of Scr. No. l3l.456, April 5. 1971, Pat. No. 3.689.456, which is a division of Ser, No, 740.853, June 28, I968, Pat No. 3.62l.0l8.  
 [52] U.S. Cl.... 260/47 EN; ll7/l28.4; lI7/l6l ZB; l6l/l84&#39;, 260/2 N; 260/2 EA; 260/l8 PF:  
 260/47 EA; 260/59; 260/923; 260/93.l;  
 Primary E.rmninerMorris Liebman Assistant E.\&#39;aminerT. Pertilla Attorney, Agent, or Firm-Peter F. Casella; James F. Mudd [57] ABSTRACT Epoxy resins can be cured with 2,6-diketo-N- carboxymethylmorpholine as the sole curing agent to produce fully cured, strong and hard compositions, which are useful as protective coatings, adhesives, and laminating, potting, and encapsulating compounds.  
 5 Claims, No Drawings CURED COMPOSITIONS OF EPOXY RESINS WITH 2,6-DIKETO-N-CARBOXYMETHYL- MORPHOLINE REFERENCE TO PRIOR APPLICATION This is a continuation-in-part of eopending application Ser. No. [3 l .456. filed Apr. 5. I97 I now L&#39;.S. Pat. No. 3.689.456. which is a division of copending application. Ser. No. 740.853. filed June 28. 1968. and now US. Pat. No. 3.621.018.  
 BACKGROUND OF THE INVENTION It has not previously been possible to prepare 2.6+ dikcto-Ncarboxymcthylmorpholine. hereinafter re ferred to as NTA anhydridc. because conventional dehydrating techniques result in a variety of side reactions. A new process has been found by which NTA anhydride can be produced. The anbydride is useful as an epoxy curing agent.  
  It is the object of this invention to provide a new composition of matter. namely 2.6-diketo-N- carboxymethylmorpholine. It is also the object of this invention to provide a process for producing the NTA anhydride. It is a further object of this invention to provide a new curing agent for epoxy resins. Other objects will become apparent to those skilled in the art from the following detailed description.  
 SUMMARY OF THE INVENTION This invention relates to NTA anhydride. the process for producing NTA anhydride and to uses of the anhydride. More particularly. this invention relates to a new composition of matter. NTA anhydride. which is produced by a process which comprises contacting nitrilotriaeetic acid in a suitable reaction media. preferably an N.N-dialkylacetamide. with a dehydrating agent. and to the uses of the NTA anhydridc so produced.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT A new composition of matter. NTA anhydride. is produced by a process which comprises contacting nitrilotriacctic acid in a N.Ndialkyl aeetamide with a dchydrating agent. The alkyl substituents can contain l to 6 carbon atoms such as methyl. ethyl. amyl. hexyl. and the like. and the preferred acctamide is N.l\&#39;-dimethyl acetamide. The nitrilotriacetic acid can be dissolved in the acetamide or in a mixture of the acetamide and the dehydrating agent. The nitrilotriacctic acid generally comprises about I to about 80 weight percent of the nitrilotriacetic acid N.N-dialkyl acetamide solution. and is preferably from about It) to about 50 weight percent.  
  Conventional dehydrating agents can be employed to convert the nitrilotriacetic acid to its anhydride. Typical dehydrating agents include organic anhydrides such as acetic anhydride. propionic anhydride. maleic anhydride. succinic anhydridc. and the like; enol esters such as isopropenyl acetate and the like; organic acid chlo rides such as acetyl chloride and the like; P and the like dehydrating agents. The preferred dehydrating agent is acetic anhydridc. The ratio of moles dehydrating agent to moles nitrilotriacetic acid can vary. from l L2 to 20. 5 It is preferred to use near the stoichiometric quantity of dehydrating agent. ic. a ratio of about (1.75 to about I moles dehydrating agent to one mole of nitrilotriacctic acid.  
  A typical synthesis procedure can comprise fitting a reaction vessel with a stirrer. nitrogen inlet tube. thermometer. and a steam jacketed partial condenser fitted to a water condenser and water trap. The nitrilotriacetic acid. N.N-dialkyl acetamide and dehydrating agent are charged into the vessel and heated under agitation and inert nitrogen spurge until the reaction reaches the desired level of completion. as conveniently measured by the acid number technique. The excess reagents can be removed by conventional techniques. such as steam distillation. and the NTA anhydride recovered by conventional techniques. such as precipitation. The reac tion mixture can be heated from about 50 to about I4()C. preferably about 70 to about l()()C. The time necessary to complete the above-described reaction can vary from 0.5 to 24 hours. although times of 2 to It] hours are preferred.  
  The NTA anhydride can be employed as a curing agent for any of those materials known in the art as epoxy resins. Included in this classification are resins such as the well-known reaction products of a dihydric phenol and a halohydrin, epoxidizcd hydrocarbons. epoxidized vegetable oils. as well as naturally occurring materials of the same type containing the oxirane ring structure. By the terms epoxy resin&#34; orpolyepoxide&#34; as used herein. is meant the compounds which contain adjacent carbon atoms to which oxirane oxygen is attached. The epoxy resins that are the reaction products of a dihydric phenol and halohydrin are generally obtained by reacting at a temperature of about 50 to I5UC at least one mole of the halohydrin. such as epichlorohydrin. glycerol dichlorohydrin. 3-chlorol .2- piopancdiol. and the like. w ith one mole ol&#39;the dihydric phenol. such as resorcinol. dihydroxy diphcnyl propane. polyhydrie phenol formaldehyde condensation products. and the like. in the presence of an alkali metal hydroxide such as sodium and potassium hydroxide or an alkaline earth hydroxide such as calcium and barium hydroxide. The epoxy resins which are formed by epoxidizing unsaturated hydrocarbons can be prepared. for example. by reacting the unsaturated polyolefin, such as polyvinylcyclohexene. polychloroprene. polyisoprene. polybutadiene, and the like. with a suitable reactant such as acetyl peroxide for several hours at an elevated temperature. Another type of epoxy resin useful in this invention are the polyepoxides derived from naturally occurring vegetable oils. or their derivatives. such as epoxidized soy bean oil. epoxidized linseed oil. epoxidized glycerol dilinoleate. and the like. Such materials are prepared. for example. by agitating the compound to be epoxidized with a peracetic acid solution. prepared from glacial acetic acid. percent hydrogen peroxide and 1 percent sulfuric acid catalyst.  
  In the practice of the invention. the NTA anhydride curing agent is mixed with the desired uncured epoxy resin at room temperature or at an elevated temperature. The curing agent is preferably incorporated in an amount from about 2 to about parts by weight per IOU parts of uncured epoxy resin. and preferably from about 51 to about 15 parts by weight. The curing temperatures yary over a wide range from to about 250C. but are preferably in the range of about l()() to about 200C. The time necessary to effect curing varies with the particular ingredients of the curing system. from several minutes to several days. however. it is preferably from about (1.5 to about 48 hours.  
  The NTA anhydride can also be used as a chemical intermediate in preparing useful chemical derivatives not easily prepared by other methods The following reactions are typical:  
 The latter acids are useful as chelating agents (see Dayatlova et al.. Russian Chemical Reviews. 48l-496 lluly. l965l).  
  The following examples are presented to further illustrate the invention. but are not intended to limit it. All parts and percentages are by weight and temperatures in degrees centigrade unless specified otherwise.  
 PREPARATION OF NTA ANHYDRIDE Example l A charge of l9l parts nitrilotriacctic acid. 348 parts N.N-dimethyl acetamide and 306 parts acetic anhy dridc were placed in a vessel equipped with a thermometer. nitrogen inlet tube, stirrer, reflux condenser. and heating means. A nitrogen sparge was employed and the vessel heated to about 90C for about 4 hours. Thereafter. the acetic acid. unreacted acetic anhydride and N.N-dimethyl acetamide were removed at 75-H4C under reduced pressure. The residue in the vessel was found to contain about 75 percent NTA an hydride.  
 Example 2 A slurry of 191 parts nitrilotriacctic acid. 1 10 parts acetic anhydride and 355 parts NN-dimethyl acetamide was stirred for about 7 hours at 80C. A small amount of the unreacted nitrilotriacctic acid was filtered from the resultant reaction mixture and most of the volatiles removed at 7U80C under reduced pres sure. The residue was stirred with 300 parts of chloroform. filtered. and the resulting solid was thoroughly washed with 300 parts of chloroformv The resulting product was dried in vacuum at ambient temperatures to produce an offwhite solid having a decomposition point of 12 l -l 24C. The product was further purified by solution in acetone, in which the nitrilotriacctic acid is insoluble and the anhydride is soluble. The product. NTA anhydride (2.o-diketo-N-carboxymethylmorpholine was obtained in about 70 percent yield and 96-97 percent purity. The NTA anhydride was further characterized by the following analysis:  
 Elemental Analysis calculated: C, tl-7; H, 4.1; N, 8..  
 found C, Mil; H, +.2;. N, 8.!  
 Nuclear Magnetic Resonance two singlet. peaks in an area ratio of 2:l are found at 3.90 and 3.60 ppm l H relative to tetramethyls&#39;ilane Titration base titrations, aqueous and non-- aqueous, showed the presence of one anhydride group and one carboxyl group, and were consistent with the assigned structure, viz  
 (I Infrared i strong absorption bands at: i710, 1776 and 1805 crn&#39; (nujol mull), showing 2 the presence of anhydride and carbexyl groups.  
 Example 3 The process of Example 2 can be repeated using a nitrilotriacetic acid which has been prepared externallyor in situ from the corresponding nitrilotriacctic acid alkali metal salt. to obtain the corresponding nitrilotriacetic acid anhydride.  
 NTA ANHYDRIDE AS AN EPOXY CURING AGENT Example 4 Ten parts of the NTA anhydride of Example 2 was mixed with l0 parts of the diglycidyl ether of Bisphe&#39; nol A at ambient temperatures. The mixture was subjected to a two-stage cure of 24 hours at C followed by 24 hours at C. A strong. hard. fully cured epoxy resin was obtained. When coated around electrical parts this cured epoxy resin provides resistance to chemicals. impact. moisture. and electricity.  
  4. A composition according to claim 3 wherein the epoxide resin comprises the reaction product of dihydroxy diphenyl propane and epihalohydrin.  
  5. A composition of matter according to claim 3 wherein said nitrilotriacetic anhydride is present in an amount from about 5 to about 15 parts by weight per l()() parts of epoxide resin.