Reaction of Urea with Citric Acid

Abstract

Reaction of urea with citric acid in aqueous solutions at molar ratios of 1 : 1, 1 : 2, and 2 : 1 and the solubility of urea citrate were studied. The data obtained can serve to optimize use of citric acid as a physiologically active substance or nitrification inhibitor and in production of liquid fertilizers containing urea.Urea is a frequent component of many liquid integrated fertilizers. Interaction of urea with citric acid can affect phase equilibria in the systems constituting liquid complex fertilizers.Urea is highly reactive. Many urea compounds obtained in reactions with mineral or organic acids are known [135]. Citric acid is a necessary component in the system of biochemical reactions of the cellular respiration. Along with other tricarboxylic acids, citric acid is contained in small amounts in mitochondria of all the cells. Another function of citric acid is to support the acid3base equilibrium and ionic composition in a living body. Citric acid is a typical chelate forming agent in reactions with metal ions. It can also inhibit nitrification [6] and hence is of interest as a component of liquid complex fertilizers.There is no reliable information on how urea reacts with citric acid. Fragmentary tentative results have been published previously [7].In this study, we examined the reaction of urea with citric acid in aqueous solutions and determined the main physicochemical properties of the reaction product.Urea CO(NH 2 ) 2 and citric acid C 6 H 8 O 7 . H 2 O were of chemically pure grade. The compositions of the substances were determined by chemical and physicochemical analyses. The nitrogen content was found in solutions and in the solid phase [8 310].A thermal analysis of solids was performed on a Du Pont Instruments 990 Thermal Analyzer at a heating rate of 10 deg min 31 .The IR spectra were recorded on a Spectrum GX (Perkin Elmer) FT-IR spectrometer in KBr pellets. An X-ray phase analysis was performed on a DRON-6 diffractometer with copper radiation and nickel filter within the 0o3166.5o range of diffraction angles with a relative error at no more than 0.5%.Mixtures of urea (Ur) and citric acid (HCit), taken in molar ratios of 1 : 1, 2 : 1, and 1 : 2, were dissolved in water taken in amounts corresponding to the weight ratio of the sum of the reactants to water of 1 : 0.25, 1 : 0.5, 1 : 0.75, and 1 : 1. The solutions were prepared at room temperature and, in a number of cases, were heated, if required, for complete dissolution of the initial substances. The results are listed in Table 1. As can be seen, a precipitate is formed at a 1 : 1 molar ratio; its chemical composition corresponds to urea citrate with a nitrogen content of 11.1 wt %. Practically no nitrogen remains in solution. At Ur : HCit = 2 : 1, a substance with~11 wt % nitrogen content precipitates, but nitrogen remains in solution in Table 1. Chemical composition of aqueous solutions containing urea and citric acid and of precipitate ÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÂÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ Ur/HCit ³ Weight ratio ³ Nitrogen content, wt % ³ ÃÄÄÄÄÄÄÄÄÄÄ...

Super water-absorbing new material from chitosan, EDTA and urea

“…However, the crosslinking of chitosan through the interaction of its amino groups with EDTA is possible, since EDTA is a tetra functional acid. The protonation of urea by organic acids resulting in compounds of varying stoichiometry and structure has also been reported (Paleckiene, Sviklas, & Slinksiene, 2005;Radell, Brodman, & Domanski, 1967). Thus, the reaction between urea and citric acid is reported to result in the formation of urea citrate (with a molar ratio 1:1).…”

“…The presence of some of the prominent peaks from EDTA (see the characterization data pertinent to EDTA blank or control reaction as well as unreacted EDTA in Supplementary Data) and urea (see the characterization data pertinent to urea blank or control reaction as well as unreacted urea in Supplementary Data) as well as new peaks in the product confirmed that a reaction had taken place between urea and EDTA. This was not surprising considering that organic acids are known to react with urea (Paleckiene et al, 2005).…”

Citric Acid

“…Similarly, heating urea and citric acid in the presence of sulfuric acid uracil-acetic acid is formed [494]. The citric acid-urea system was also investigated by Paleckiene et al [603], but in the context of liquid fertilizers containing urea and the influence of citric acid on corresponding phase equilibria. It was observed by Brettle [604] that citric acid reacts with chloral Cl 3 CCHO, to give citric acid chloralide (actually, from condensation of citric acid with chloral hydrate in concentrated sulfuric acid).…”

Fabrication and Characterization of Nano-Hydroxyapatite\ Chitosan Biocomposites with and without Citric Acid Addition

“…Afterwards, the compressive strength was decreased to (12.84 MPa) as in the HAC3 composite as a result of the reduction of interaction between two matrices. The values of compressive strength of all HAC composites were higher than that of the prepared HA (9.66 MPa) proving the role of chitosan polymer matrix in enhancement of the bonding strength between the HA particles within the composite (14) . The compressive strength of the HAC/citric acid composites increased especially in the case of HAC2/citric acid composite recording 30.5 MPa in comparison with the HAC composites.…”

“…at 1028, 603 and at 569 cm -1 were reduced compared to the original bands in the HA powder proving the coating effect, especially in the case of the HAC2 composite. Also, the bands of chitosan in the spectra of HAC composites such as OH at 3446 cm -1 , CH at 2921 cm -1 and amide I at 1652 cm -1 were reduced compared to original polymer denoting interactions through hydrogen bonds as follows: (1) The OH of HA and chitosan, (2) the calcium of the HA with OH or amino group of chitosan, (3) the phosphate of the HA with the amino group of chitosan (14) .…”