Problematic amines

Another class of problematic amines are a-amino nitriles, which are readily accessible from ketones, amines, and cyanide. Like a-amino acids, these amines are electronically deactivated and less basic and nucleophilic than purely aliphatic amines, and are therefore difficult to acylate. Some a-amino nitriles or the corresponding acylated derivatives can, furthermore, decompose into imines and cyanide if reaction temperatures are too high or if the bases used are too strong (Scheme 7.11). 

Amines are nucleophilic and easily oxidized. Primary and secondary amino groups are also sufficiently acidic that they are deprotonated by many organometallic reagents. If these types of reactivity are problematic, the amino group must be protected. The... 

In the analysis of isocyanuric acid, a stabilizer used in swimming pools, ion exchange separation on an Omnipac PCX-500 was used to separate isocyanuric acid from ammelide, ammeline, and melamine (Figure 4).104 Since ammelide has one primary amine, ammeline two, melamine three, and isocyanuric acid none, derivatization and RPLC would have been problematic. 

Problematic functional groups, however, are thioethers and disulfides [28] as well as free amines which poison catalysts of type 1 [4c]. In case of amines this problem is easily solved by choosing either an appropriate protecting group for nitrogen (e.g. amide, sulfonamide, urethane), or simply by protonation since ammonium salts were found to be compatible with 1 [4c]. As will be discussed in Sect. 4, free amines can also be metathesized in supercritical C02 as the reaction medium [7]. 

Establishing the elemental composition based on the isotopic peaks may be problematic if, for example, the sample contains impurities with the masses in the region of the molecular ion cluster. In the El mass spectra of amines, alcohols, acids, and some other classes of organic compounds there is often a peak of [M + H]+ ion. It distorts the isotopic picture. It is worth mentioning as well that in real experimental conditions the peak intensity may vary slightly in each... 

The use in consumer products of azo dyes that yield carcinogenic amines under reductive conditions is illegal in Germany. Detection of such carcinogenic amines in textiles is problematic, and a method was proposed combining TLC, automatic multiple development... 

Cyanation of aldehydes and ketones is an important chemical process for C C bond formation." " Trimethylsilyl cyanide and/or HCN are commonly used as cyanide sources. The intrinsic toxicity and instability of these reagents are problematic in their applications. Acetyl cyanide and cyanoformates were used as cyanide sources in the enantioselective cyanation of aldehydes catalyzed by a chiral Ti complex and Lewis base (Scheme 5.31)." The Lewis base was necessary for the good yields and selectivities of these reactions. The desired products were obtained in the presence of 10mol% triethyl amine and 5mol% chiral titanium catalyst (Figure 5.14). Various aliphatic and aromatic aldehydes could be used in these reactions. 

Like TATP, detection of HMTD is problematic. HMTD, being an amine, does give off a unique odor. The smell emitted by HMTD has been likened to that of fish. As it gets older, the odor gets more predominant and unpleasant. 

Woodhouse described a degradable polyurethane prepared with a novel amine chain extending agent. As with the insertion of lactic acid into the backbone, bio-degradability was achieved, but the fragments appeared problematic. Thus, while biodegrading polyurethanes are fairly simple to prepare, one must be aware of the product to which a polyurethane degrades. The use of TDI as the isocyanate would clearly raise concerns from the FDA. 

Although many of the details remain to be clarified, transfer of nitrosyl groups onto preformed iron-sulfur frameworks of the natural type is well established (107,108). The transfer of nitrosyl groups from iron-sulfur-nitrosyl complexes to atoms other than iron is more problematical, as reported work on the ability of these complexes to nitrosate secondary amines RR NH, with formation of secondary nitrosamines RR NNO, has provided conflicting conclusions. 

While the determination of total lysine is rather straightforward, the determination of free or available lysine is more problematic. In this situation, the term free is meant to imply that the e-amine of the lysine side chain has not reacted with various components of the sample matrix (most commonly carbohydrates via Maillard browning). This is important because reaction of the e-amine can render lysine nutritionally unavailable and the nutritive value for that protein is then diminished if lysine is the limiting amino acid (which is often the situation with soy proteins). While enzymatic digestion in the human gut may not release the modified lysine in a nutritionally available state, often these lysine adducts are labile to the standard acid hydrolysis in 6N HC1 at 110°C. This results in total lysine values that overestimate the amount of nutritionally available lysine. 

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