Urea inclusion compounds

Canals in the urea inclusion compounds have a diameter of approximately 5.25 A. 

Linear guest molecules are included along these canals in an extended planar zig-zag conformation. Branched molecules are generally excluded unless branching occurs near the end of a long linear chain, but aromatic derivatives can be included if they have a long alkyl chain 38). The review article by Takemoto and Sonoda 21) contains an excellent survey of the types of molecules known to form urea inclusion compounds and of the means used to study their detailed conformations and thermal motion. 

Thermal Changes and Structural Modifications of Urea Inclusion Compounds... 

Yet another type of canal structure has been reported for the urea inclusion compound of 1,4-dichlorobutane 51). Even though the canals are pseudo-hexagonal in dimension, there is a significant difference in their symmetry. The host lattice is orthorhombic, space group Pbcn. The difference lies in the directions of the six pseudo-3j helices of host molecules around the walls of each canal the sequence is cyc/o-RRRLLL, as opposed to cyc/o-RRRRRR in the hexagonal inclusion compounds and cvc/o-RLRLRL in the rhombohedral. This orthorhombic host structure probably occurs also in the urea inclusion compounds with 1,5-dichloropentane and 1,6-dibromohexane 51). 

Well-developed applications 19-21) of urea inclusion compounds have been in the areas of detergents, dewaxing and petroleum chemistry. Some recent novel advances include the use of the peroxydodecanoic acid-urea inclusion compound in a laundry bleach product60 and in the purification of insect pheromones61 62. ... 

Irradiating nonan-5-one as a urea inclusion compound affords only one cyclobutanol isomer in a much higher yield (as compared to both diastereomers in solution). Apparently the cyclobutanol also remains an included molecule.7... 

Recently, Radell, Connolly and Raymond [7] prepared normal pentyl, hexyl, heptyl and octyl perchlorates from the corresponding alkyl iodide and silver perchlorate. The oily esters were purified as urea inclusion compounds. 

Single crystal of urea inclusion compound (originally with I.S-dibromooctane guest ... 

One of the main interests in urea inclusion compounds is their potential application in the separation of linear and branched hydrocarbons in the petroleum industry. Because the channel diameter is only slightly larger than the van der Waals diameter of a linear hydrocarbon, only a small amount of branching can be tolerated. Whether a particular urea inclusion compound will form or not may be assessed simply by comparison of the channel size with the diameter of the guest. For example, benzene is... 

Figure 7.8 Host and guest repeat distances in urea inclusion compounds are not necessarily the same.

Brown, M. E., Hollingsworth, M. D., Stress-induced domain reorientation in urea inclusion-compounds. Nature 1995, 376, 323-327. 

Bombykol was for the first time prepared by Butenandt using the Wittig reaction of 2-hexynylidene-triphenylphosphorane with 9-formylnonanoic ester. The resulting (Z)- resp. ( )-10-hexadecen-12-ynoic acid esters were resolved by urea, the ( )-isomer hydrogenized with Lindlar catalyst and reduced with lithium aluminium hydride. Further purification via the urea inclusion compound and low-temperature crystallization gave (10F,12Z)-10,12-hexadecadien- l-ol 186,187). 

Recently, it has been shown by Hollingsworth et al. that urea inclusion compounds of formula X(CH2)6CN/urea (X = Cl, Br) undergo reversible crystal-... 

A laser flash study of the photoreactions of hexan-2-one and 5-methylhexan-2-one has provided evidence for the existence of the triplet 1,4-biradicals produced by the y-hydrogen abstraction typical of Norrish Type II reactivity. The photochemical behaviour of the alkanone, nonan-5-one, in urea inclusion compounds has been studied. In solution, irradiation of nonan-5-one yields hexan-2-one, propylene, and two cyclobutanols. In the clathrate, the fragmentation products were essentially the same but only one cyclobutanol was observed. The cyclization fragmentation ratio was established as 0.67, compared with 0.32 in methanol. The authors suggest that the CIS-cyclobutanol has less stringent rotational requirements and that it is this isomer (43) which is formed in the clathrate. 

Urea inclusion compounds Fractionation of polyunsaturates from saturates Downstream processing of lipase-catalyzed PUFA-enriched FFA... 

Hayes, D.G. Purification of free fatty acids via urea inclusion compounds. In Handbook of Functional Lipids Akoh, C.C., Ed. CRC Press Boca Raton, FL, 2005 77-88. 

Fig. 17. Schematic of the nonadecane/urea-inclusion compound. From left to right single-crystal experiment by rotation around the channel axis. Critical inhomogeneous linebroadening on approaching the transition temperature from above, with a lineshape invariant by rotation around c hole burning in the last spectrum proves the inhomogeneous nature of the broadening. Schematic of rotation patterns that gives the chain orientation in the low-temperature phase.

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