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United States Patent Office E Unitede States- Patent- Office 3,845,059E. 1. 2 The reaction of biuret with diethanolamine to form PREPARATION OF N,N'-DIETHANOL3,845,059 PIPERAZINE N,N'-diethanol piperazine can be illustrated as follows: Alvin F. Beale, Jr., Lake Jackson, Tex., assignor to The Dow Chemical Company, Midland, Mich. 2(HOCH)NH -- NH2CONHCONH --> No Drawing. Filed June 19, 1972, Ser. No. 264,704 5 CHO Int, C. C07d51/70 U.S. C. 260-268. SY 8 Claims /N al-woman-mamm CH, CH, ABSTRACT OF THE DISCLOSURE + 2CO. 1 + 8NHat Diethanolamine is reacted with urea or a urea pyrol- lo Y yzate (e.g. biuret, triuret, or cyanuric acid) to form N,N'-diethanol piperazine. The following chart illustrates the balanced stoichiom BACKGROUND OF THE INVENTION la etry for reacting diethanolamine with urea, biuret, triuret, N,N'-diethanol piperazine has been previously prepared and cyanuric acid. Reaction products Moles of Empirical Moles N,N'- Moles of formula of of diethanol Moles Moles (HOCH)NH Name of reactant reactant reactant piperazine of Co2 of NH3 2---------------------- Urea------------------------ CHNO 2 2 4. 2- ---. Biuret---. C2HNO2 2 3 6-- --- Triuret.----- ... C3HNO3 2 3. 6 8 6.----- ... Cyanuric aci - C3H3NO3 2 3. 6 6 by the condensation of piperazine with ethylene chloro- The reaction has been found to be specific for dieth hydrin as reported in J. Am. Chem. Soc., Vol. 55, p. 3823 anolamine since analogous dialkanolamines do not give (1933). The compound has been reported to have phar- corresponding dialkanol-substituted cyclic structures con macological properties as an anesthetic or sedative in 30 taining nitrogens within a carbon ring. Heterocyclic Compounds, Vol. 6, published by John The reaction of diethanolamine with reactants urea, Wiley & Sons, Inc. of New York. biuret, triuret, or cyanuric acid may be carried out using SUMMARY OF THE INVENTION only one of said reactants or may be a combination of two or more of said reactants. It has now been found that N,N-diethanol piperazine 3.5 The reaction may be carried out in an inert solvent is efficiently and inexpensively prepared by reacting di- or diluent or may be carried out using an excess of the ethanolamine with urea or a urea pyrolyzate. diethanolamine as the reaction medium. Urea pyrolyzates are obtained by thermally condensing When excess diethanolamine is employed as the reac urea to form, principally, biuret, triuret, and/or cyanuric tion medium, it can be cycled back to the reactor and em acid; ammonia is driven off as the urea condenses. Other ployed along with make-up diethanolamine and fresh cyclic urea pyrolyzates (besides cyanuric acid) such as urea or urea pyrolyzate added. When an inert carrier or isocyanuric acid, ammelide, ammeline, etc. are also pre- solvent is employed as the reaction medium, it can be pared by autocondensation of urea. The thermal con- re-cycled back to the reactor after the product is sub densing of urea to form pyrolyzates is a well known re stantially removed. action and requires no further description herein. In 45 It will be understood by persons skilled in the art that Chemical Reviews, Vol. 56, pp. 95-197, there is a review inert carriers useful in the present invention may be sol titled "Biuret and Related Compounds” by Frederick vents for either the diethanolamine or the urea (or urea Kurzer which describes the condensation of urea to biuret pyrolyzates) or both. They may also be solvents for the and other compounds. 50 desired product (viz., N,N'-diethanol piperazine). It is also easily understood that the solubilizing ability of an DETALED RESSESN OF THE inert carrier will usually vary with the temperature. It is advisable to perform the present process in a medium in The reaction of urea with diethanolamine to form which the desired product is easily precipitated while N,N'-diethanol piperazine can be stoichiometrically illus- keeping the reactants in a non-precipitated state. Inert trated by the following balanced equation: 55 liquids which are not solvents for the reactants or the desired product may be employed as the reaction medi 2(HOCH)NH -- 2NH2CONH - um, but are not preferred. CHO . The reaction product, N,N'-diethanol piperazine, is easily precipitated from the reaction solution by cooling /S 60 or by adding a non-solvent which is miscible with the pH, (H, 2CO 4N reaction solvent, depending on the situation. Preferably, CH, CH -- f -- s the reaction is carried out in a medium in which the re N/ actants are soluble, but in which the desired product (di N ethanol piperazine) will precipitate when formed or when CEO cooled, - - - - - 3,845,059 3 4. The ratio of the reactants to each other is not critical the mixture was cooled and it was filtered out and washed as the reaction proceeds according to the stoichiometrical with acetone. The dried ppt. weighed 1 lb. 12 oz. and equation illustrated hereinbefore. Ordinarily an excess of was analyzed as N,N'-diethanol piperazine. The yield is the diethanolamine is employed, either because the di calculated as about 61% (theoretical). ethanolamine is to serve as the reaction medium or be cause it is usually more soluble, in whatever reaction EXAMPLE 3 medium is used, than the urea (or urea pyrolyzate) or The filtrate from Example 2 above (12 lbs., 3 oz.) was the desired product. This helps in separating the product mixed with 1 lb. 7 oz. of tetraethylene glycol dimethyl from residual diethanolamine. It is best to select condi ether, 1 lb. 3 oz. of urea, and 2 lb. 2 oz. of diethanolamine. tions in which all the urea or urea pyrolyzate is con The mixture was heated under a N purge, with stir sumed, thus simplifying the purification of the product. 10 ring, at 135 C. for 24 hours, then at 145 C. for 19 As the reaction progresses, CO and NH3 are evolved hours. The mixture was cooled, the precipitate was filtered and released from the reaction. An inert gas purge or out, washed with acetone, dried and found to weigh 1 lb. sparge may be employed to speed the release of CO2 and 6 oz. It was analyzed as N,N'-diethanol piperazine. The NH3. Reduced pressure may also be employed in some 5 yield is calculated as about 79.5% (theoretical). instances to speed the release of the CO2 and NH3 from EXAMPLE 4 the reaction. , Even though the reaction will proceed at sub-atmos A stirred mixture of 105 gms. of diethanolamine and pheric, atmospheric, or super-atmospheric pressures, at 60 gms. of urea was heated under a N purge at 150 C. mospheric pressures are preferably employed for econom for about 7 hours. During this time the evolving NH ic reasons and also to provide for easy purging of the 20 was passed through an acid scrubber and was sufficient to evolved CO2 and NH3. Super-atmospheric pressures re neutralize 225 ml. of 7.6N HSO4. tard the release of CO2 and NH from the reaction mix The mixture was cooled and 100 ml. of triethylene gly ture, thus are not preferred. col dimethyl ether was added. The precipitate was filtered As will be readily apparent to those skilled in the art, out and washed with acetone. The amount of dried prod the vapors and gasses leaving the reactor can be easily 25 uct obtained (N,N'-diethanol piperazine) represented a trapped by conventional methods either for re-cycling or 15%' yield (theoretical). for preventing contamination of the ambient atmosphere. Broadly speaking the reaction can be carried out at EXAMPLE 5 temperatures ranging from about 70° C. to about 268 30 A stirred mixture of 130 gms. of diethanolamine and C. (the boiling point of diethanolamine). At 70° C. the 60 gms. of urea was heated under a N purge at 150 C. reaction is very slow and it would take many days to get for 8 hours. During this time the evolving NH neutralized an appreciable yield of desired product. For best opera 235 ml. of 7.6N HSO4 in a scrubber. After cooling, tion, a range of about 110-175 C., preferably about 50 ml. of triethylene glycol dimethyl ether was added, 130-165 C. should be used for urea, biuret, and triuret. the precipitate was filtered out, washed with acetone, The reaction proceeds as slower rates at lower tempera and dried. The dried ppt., analyzed as N,N'-diethanol tures; at higher temperatures the reaction is accelerated piperazine, weighed 24.5 gms. which was about 28% but the tendency to form undesirable side-products is also yield (theoretical). encountered. EXAMPLE 6 When cyclic urea pyrolyzates, such as cyanuric acid, 4. In similar manner to the above Example 5, 158 gms. are used in the reaction, the temperature should be main of diethanolamine and 60 gms. of urea were reacted at tained in the range of about 165-265 C., and prefer 50° C. for 22 hrs. with 255 ml. of 7.6N HSO being ably about 215-240° C. Here again, one finds that at neutralized by the evolving NH3. Mixture was cooled, lower temperatures the reaction is quite slow and at higher 100 ml. of triethylene glycol dimethyl ether was added, temperatures, the formation of unwanted side products 45 the precipitate was filtered out, washed with acetone, is likely to be encountered. and dried. The dried product (N,N'-diethanol piperazine) In those instances in which an inert carrier is used as weighed 33 gms. which represented about 38% yield the reaction medium, the boiling point of the carrier (theoretical). may limit the reaction temperature. For this reason, a EXAMPLE 7 carrier should be selected which has a boiling point at least as high as the desired operating temperature.
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