Hindered amines groups

GRAFTING OF HINDERED AMINES GROUPS ON EPDM AND POLYOCTENAMER VIA PHOTO-HYDROPEROXIDATION... 

Grafting of Hindered Amine Groups on EPDM and Polyoctenamer via Photo-... 

Polyisobutylene has the chemical properties of a saturated hydrocarbon. The unsaturated end groups undergo reactions typical of a hindered olefin and are used, particularly in the case of low mol wt materials, as a route to modification eg, the introduction of amine groups to produce dispersants for lubricating oils. The in-chain unsaturation in butyl mbber is attacked by atmospheric ozone, and unless protected can lead to cracking of strained vulcanizates. Oxidative degradation, which leads to chain cleavage, is slow, and the polymers are protected by antioxidants (75). 

Sterically hindered amines often tend to form ureas with (BOC)20, because of isocyanate formation. The problem can be avoided by reacting the amine with NaHMDS and then with (BOC)20. The isocyanates can also be converted to the BOC group by heating with r-BuOH. When other alcohols are used, the corresponding carbamate is produced. ... 

The hindered secondary amines can be highly effective photostabilizers for various polymers (]+.,5.,.6) Various hindered amines have been shown to retard oxidation, but most share the common feature of being secondary or tertiary amines with the a-carbons fully substituted. The most widely exploited representatives of this class are based on 2,2,6,6-tetramethylpiperidine either in the form of relatively simple low molecular weight compounds, or more recently as backbone or pendant groups on quite high molecular weight additives ( i.,5.,6). The more successful commercial hindered amines contain two or more piperidine groups per molecule. Photo-protection by tetra-methylpiperidines (near UV transparent) must result from the interruption of one or more of the reactions 1 to 3. Relatively recent results from our own laboratories, and in the open literature will be outlined in this context. 

In the present study possible modes of action of a relatively new class of light stabilizers, the Hindered Amine Light Stabilizers (HALS, tetramethylpiperidine derivatives, TMP) will be discussed. Certain members of this group have a light stabilizing effect superior in many fields of application to that of previous additives. They are effective in both thick layers and fibers13 12. 

In order to explore the generality of this new domino reaction the conversion of various primary amines with 2-341 and the cyclohexane analogue was investigated (Scheme 2.81). For example, the reaction proceeds with high yields when benzyl- or (2-phenylethyl)amine are used (entries 1 and 2). In comparison, sterically more hindered amines such as 2-butylamine produced much lower yield (entry 4) Furthermore, the reaction tolerates other functional groups, such as an unprotected hydroxyl group (entry 5), and variation of the enone ring size is possible (entries 6 and 7). More recent results have revealed that the addition of Sn(OTf)2 or In(OTf)2 makes the transformation more reliable. 

The group of Caddick has described the synthesis of functionalized sulfonamides by microwave-assisted displacement of pentafluorophenyl (PFP) sulfonate esters with amines (Scheme 6.159) [306]. Their ease of handling due to their higher crystallinity, along with their long shelf-life and their ability to react under aqueous reaction conditions, makes these an attractive alternative to sulfonyl chlorides. The microwave-assisted reaction of alkyl PFP esters with amines is a facile process which proceeds cleanly and in good yields with a number of different amines, including primary, secondary, and sterically hindered amines, and anilines. Optimum condi-... 

More recently, Polish chemists have reported a synthesis of both aryl and aliphatic secondary nitramines by treating amine substrates with ethyl magnesium bromide followed by reaction with n-butyl nitrate (Equation 5.8). This method, which uses nonpolar solvents like hexane or benzene, has been used to synthesize aliphatic secondary nitramines, and At-nitro-A-methylanilines which otherwise undergo facile Bamberger rearrangement in the presence of acid. The direct nitration of At-unsubstituted arylamines usually requires the presence of an electron-withdrawing group. Reactions are retarded and yields are low for sterically hindered amines. 

The is-boron enolates of some ketones can be preferentially obtained with the use of dialkylboron chlorides.17 The data in Table 2.3 pertaining to 3-pentanone and 2-methyl-3-pentanone illustrate this method. Use of boron triflates with a more hindered amine favors the Z-enolate. The contrasting stereoselectivity of the boron triflates and chlorides has been discussed in terms of reactant conformation and the stereoelectronic requirement for perpendicular alignment of the hydrogen being removed with the carbonyl group.18 The... 

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