Raman studies of cyanate: Fermi resonance, hydration and hydrolysis to urea

Abstract

. Rarnan spectra were measured for potassium cyanate in the solid phase and as aqueous solutions in H20 and D20 for freshly prepared and for aged solutions. The results indicated that the assignment of the Fermi doublet, v, and 2v2, for solid potassium cyanate was reversed from the assignment for the aqueous solution. The Fermi doublet has an associated pair of hot bands at 1191 and 1315 cm-' which originate from the 638 cm-I v, state, 010. Assignment of the hot bands was confirmed by studies of solid potassium cyanate at liquid-N, temperature, room temperature, and at 473 K. Raman spectra of aged aqueous potassium cyanate revealed that the cyanate ion hydrolyzed slowly and spontaneously at room temperature (even without added ammonium) to produce urea and a carbamate, carbonate equilibrium mixture in parallel reactions. Hydrolysis of cyanate in aqueous ammonium chloride solution resulted in almost total conversion of cyanate to urea. The reaction was not reversible under ambient conditions. Differences in peak frequencies and halfwidths were observed for the cyanate dissolved in Hz0 compared to solutions in D,O. The results provide evidence for strong hydrogen bonding of cyanate to water and are consistent with greater structure in the D20 solution. Theoretical ab initio calculations indicated that the water molecules hydrogen bond well at both the oxygen and nitrogen atoms of cyanate although the hydrogen bond to nitrogen was found to be slightly stronger.MURRAY H. BROOKER et NANPING WEN. Can. J. Chem. 71, 1764Chem. 71, (1993. On a mesure les spectres Raman du cyanate de potassium en phase solide et en solutions aqueuses dans le H,O et le D,0 pour des solutions frafchement prkparees ainsi que pour des solutions qui avaient vieillies. Les resultats obtenus indiquent que l'attribution du doublet de Fermi, v, et 2v2, pour le cyanate de potassium a 1'Ctat solide doit &tre inverse par rapport a ce qui est observe en solution aqueuse. La doublet de Fermi est associk a une paire de bandes chaudes 2 1191 et 1315 cm-I qui ont leur origine dans l'etat v2, 010, a 638 cm-I. On a pu confirmer l'attribution des bandes chaudes par des etudes sur le cyanate de potassium solide la temperature de I'azote liquide, a la temperature ambiante et a 473 K. Les spectres Raman des solutions aqueuses du cyanate de potassium qui ont vieillies rkvklent que I'ion cyanate s'hydrolyse lentement et spontanement a la temperature ambiante (mCme sans addition d'ammonium) pour former de l'uree et un melange a l'equilibre de carbamate/carbonate provenant de reactions parallkles. L'hydrolyse du cyanate en solution aqueuse de chlorure d'amrnonium provoque une conversion presque globale du cyanate en uree. La reaction n'est pas reversible dans les conditions ambiantes. On a observe des differences dans les frequences et les demi-largueurs des bandes du cyanate dissous dans le H20 par rapport aux solutions dans le DzO. Les resultats suggkrent qu'il existe de fortes liaisons hydrogenes entre le cyanate et l'eau et ils sont en accord avec la plus gran...

Detailed modeling of the evaporation and thermal decomposition of urea‐water solution in SCR systems

“…Reactions R1 and R10 involve "solid" and "aqueous" urea, which behave differently towards thermal decomposition [60]. Previous studies [61][62][63] indicate that the backward step of R1 can be of significance in our conditions. However, for simplicity purposes, we choose to include only the forward step of R1.…”

Single-Crystal X-Ray Diffraction Study of Na[OCN] at 170 K and its Vibrational Spectra

“…The bending mode δ is degenerate in the IR spectrum at 626 cm −1 while in the Raman spectrum this mode is split and observed at 626 and 638 cm −1 . As observed for K[OCN] [13], the symmetric stretching mode ν sym couples with the first harmonic overtone of the bending mode 2δ and shows Fermi resonance [13,14] which occurs both in the IR and the Raman spectrum. By this effect, the overtone usually grows in intensity while the fundamental vi- bration loses intensity.…”

“…The shift is in both spectra nearly the same, and the Fermi-doublet shows at 1215 and 1305 cm −1 . The relative intensities and the seperation of the maxima depend on how closely the undisturbed frequencies fall, and these can be calculated with the following expression [13,14]:…”

Rate constants for cyanate hydrolysis to urea: A Raman study

“…rating the mixture to dryness. Normally, it is assumed that In the present study Raman spectra of aged aqueous soammonium cyanate was prepared in an ion-pair reaction [4] lutions of a mixture 2. followed by rearrangement of ammonium cyanate to form urea (reaction [5]). …”

“…As part of a comprehensive study (3) of aqueous solutions of small molecules which contain N, C, 0 , and H the Raman spectrum KOCN has been measured for the aged aqueous phase. A full account of band assignments, Fermi resonance, and hydration of aqueous cyanate has been presented elsewhere (3,4).…”