Ammonia from labeled

Evidence for symmetrical intermediates such as benzyne cannot be established by quantitative analysis of the reaction mixture unless a labelled starting substance is used. By applying labeling techniques, Roberts and his collaborators obtained results which indicated that benzyne (13) occurs as an intermediate in the amination of chlorobenzene with potassium amide in liquid ammonia. From chlorobenzene-1-C (12) about equal amounts of anUine-l-C (14) and aniline-2-C (15) were formed. More or less probable alternative... 

Interestingly, hydroboration-amination as an isotope incorporation methodology has led to the synthesis of isomerically pure 13N- and 15N-labeled primary amines from labeled ammonia [23-25] (Scheme 8). These labeled amines are valuable intermediates in pharmacology. 

Ionized primary enamines of low energy may also be reaction intermediates in the loss of ammonia. Scheme 34 shows a mechanism proposed for the extensive loss of ammonia from low-energy ionized 3-amino steroids. Enamine 63 may lose ammonia after two successive 1,4 H-transfers. The participation of the H at C,5, has been established by D-labelling. Only higher energy ions lead to mjz 82 fragment ions through the ionized dienamine 64,... 

The enzyme phenylalanine ammonia lyase (EC 4.3.l.S) catalyzes elimination of ammonia from phenylalanine 297a to yield ( )-cinnamic acid 309a, X = H, and various research groups (303,305,306,309) have shown that the 3-pro-S hydrogen, Hp, is eliminated in the process by using the synthetic samples of stereospecifically labeled phenylalanine. Elimination of ammonia is therefore... 

The computer model was used to simulate the uptake and loss of label from the rat brain following a bolus injection of [ N]ammonia via the right internal carotid artery (Figure 2). The simulation predicts rapid loss of unmetabolized [ N]ammonia from the rat brain over the first 10 s followed by a much slower loss of [ N]glutamine. The simula-... 

Ammonia labeled with N is prepared from labeled NH Cl and KOH in an apparatus especially suitable for smaller quantities (Fig. 176). N -SH Cl (1.2 g.) is introduced via inlets into small flask k and mixed with 5 ml. of water. Approximately 4 g. of KOH pellets is introduced via inlet ft and about 8 g. via d the glass lugs prevent their descent. The condensation trap/ is cooled in liquid nitrogen after tubes a, ft andd are sealed by fusion, and the pressure is decreased to 450 mm. Stopcock ft. can remain closed during the gas evolution in spite ofthe pressure increase, provided the gas... 

Ammonia borane acts as a metal-free reductant for ketones and aldehydes in methanol solution, via the MeOH BHj complex.In THF, borate esters are the only organic products, with dissociation of ammonia from ammonia borane being rate determining. H-, B-, and C-NMR studies, deuterium labelling, and kinetic isotope effects are... 

A Figure 16.3 The HCI(g) escaping from concentrated hydrochloric acid and the NHsCfif) escaping from aqueous ammonia (here labeled ammonium hydroxide) combine to form a white fog of NH4CI(s). 

A process for producing ammonia from air, water, and methane was outlined in this chapter. Draw the flowsheet for the entire process. Label the units and list the components in each stream. Where appropriate, use the proper symbol to identify a unit operation. Finally, improve the energy efficiency of the process by adding heat exchangers before the air condenser and the ammonia reactor. 

MIT. Autoradiography of two-dimensional chromatograms (solvent, phenol-collidine) of alkaline hydrolyzates of whole glands of rats treated with I showed the presence of a few spots of unknown substances (47), one of which was identified as 3-monoiodo-L-tyrosine (8,62,65). The specific activities of the MIT spot (solvent, collidine-ammonia-water) at intervals after injection of labeled iodide showed that MIT is the precursor of DIT and of Tx (65,70). These results were not completely convincing due to the great destruction of DIT by alkaline hydrolysis they have been confirmed, however, by the study of the amino acids freed from labeled thyroglobulin by enzymic hydrolysis under conditions which permitted no deiodination (38). 

The administration of N -2,6-diaminopurine resulted in the appearance of in RNA and DNA guanine, and in adenine to a lesser degree (203). Later studies with C -2,6-diaminopurine showed that only the guanine, and not the adenine was labeled (204). The incorporation of N into adenine in the first instance was probably due to purine synthesis from labeled ammonia, which would have been formed from catabolism of the administered labeled compound. Since 2,6-diaminopurine has not been found as a natural product, it is difficult to evaluate its metabolic importance in the conversion of dietary adenine to nucleic acid guanine. 

An alternative synthesis of amide ions is the treatment of amines with alkali metals. Alkali metals dissolve in amines (albeit relatively slowly) with the evolution of hydrogen and the formation of amine salts (much as they dissolve in water and alcohol, furnishing H2 and metal hydroxides or alkoxides. Section 9-1). For example, sodium amide can be made in liquid ammonia from sodium metal in the presence of catalytic amounts of Fe, which facilitates electron transfer to the amine. In the absence of such a catalyst, sodium simply dissolves in ammonia (labeled Na, liquid NH3 ) to form a strongly reducing solution (Section 13-6). 

The hairpencil secretion of the adult male bertha armyworm, Mamestra configurata, contains 2-phenylethanol (465, 466). Radioactive labelling experiments with male pharate adults indicated that it is synthesized from phenylalanine (466). The proposed biosynthetic pathway entails the irreversible loss of ammonia from phenylalanine to yield tra s-cinnamic acid, decarboxylation to styrene, and hydration of the styrene to yield 2-phenylethanol (466). The production of 2-phenylethanol from phenylalanine is well established in microorganisms (467—470). 

The mechanism outlined above is supported by experimental findings. An intermediate 5 has been isolated, " and has been identified by and N-nuclear magnetic resonance spectroscopy. Side-products have been isolated, which are likely to be formed from intermediate 4. N-isotope labeling experiments have shown that only the nitrogen remote from the phenyl group is eliminated as ammonia. 

Polythene wash bottles are sometimes charged with wash liquids other than water. Attention must be drawn to the fact that the components of some wash solutions may pass into the polythene and may be released into the space in the bottle when it is set aside repeated fillings and rinsings may be required to remove the chemicals from the bottle. It is safer to label the wash bottle and to reserve it for the special wash liquid. Such wash solutions include a weakly acid solution saturated with hydrogen sulphide, dilute aqueous ammonia, saturated bromine water, and dilute nitric acid. 

Xylose-rich pectic polysaccharide was extracted from defatted and protein-free cell wall preparation (5) using HCl solution (pH 1.6) at 85° C for 4 h. The extract was adjusted to pH 5.0 with ammonia, concentrated on a rotary evaporator under reduced pressure at 40°C, and precipitated with 5 volumes of 96% ethanol. After washing twice with 80% ethanol and drying in an air circulated oven at 40°C for 2 h, the pellet was ledissolved with distilled water and then precipitated with 4 vols 96% ethanol. Before the pellet was gently ground, the precipitated pellet was washed twice with 70% ethanol and dried at 40 ° in an air circulated oven for 16 h. The resultant white powder was labelled "xylose-rich pectic polysaccharide" and stored in a refrigerator. 

FIGURE 10.13 The TLC profiles of labeled peaks isolated from [U- C]ascorbic-acid-modified calf lens protein obtained from Bio-Gel P-2 chromatography. Peaks 2 to 7 were spotted on a preparative silica gel TLC plate and developed with ethanol/ammonia (7 3, v/v). The fluorescence in each lane was detected by irradiation with a Wood s lamp at 360 nm, and the pattern of radioactivity was determined by scanning the plate with AMBIS imaging system. (Reprinted with permission from Cheng, R. et al., Biochim. Biophys. Acta, 1537, 14-26, 2001. Copyright (2001) Elsevier.)... 

---