Hindered phenol series

Table 1. Antioxidant Effectiveness of the Hindered Phenol Series (III) at the Same Molar Concentration (2 x 10 M) at 140 °C...

One of the present authors (31) has developed a series of additives which combine the features of both free radical inhibitors and flame retardants of the tetrabromophthalimide or chlorendic imide type with hindered phenol antioxidant structures such as the following compounds ... 

In general, the introduction of spatially hindered phenols into coordination compounds may produce stable free-radical forms [138b—140]. A series of metal complexes with redox ligands, containing derivatives of 2,6-di-t-butylphenols n- or a-connected, or vicinal fragments in the coordination environment of the central metal atom, were synthesized in this way 7i-aryl [141], Tt-cr-allyl [142] compounds, nitrile complexes [143], metal glioximates [144], salicylaldiminates [145,146], por-phyrines [147-149], and phthalocyanines [150,151],... 

To determine how a strong insolubility promoter like cadmium stearate, and a strong insolubility retarder like 2,6-di-ferf-butyl-4-methyl-phenol affects the resin when both are present, a series of one-hour oven-aging tests were run. The results are given in Table IV. Even at very low cadmium concentration the insolubilization effect is great and is only slightly altered by adding the hindered phenol. 

An ionic 2-chloro-l,3,2-diazaphospholene (72) was prepared from a silicon precursor (73). Since the saturated analogue 74 was covalent, the phosphenium ion 72 is probably stabilised by having an aromatic 6n electron structure. The phosphadiazonium compound 75 with a sterically hindered phenol or aniline gave the phosphenium ions 76 this constitutes a new preparative route to phosphenium ions. A series of phosphenium ions (77), stabilised by two intramolecular dative P-N bonds, has been prepared, and the X-ray crystal structure of one (77, X = H, Y = PFg) determined. ... 

Some of the preparative methods for alkyl phenols and their reactions are unique to this class and both therefore warrant separate treatment from the parent compound. These features are even more prevalent in the hindered phenols a group of substances first synthesised less than half a century ago. In this account the synthesis of alkylphenols bearing purely methylenic side-chains in the benzenoid, naphthalenic and polycyclic series are considered first. Alkylphenols with side-chains containing oxy or alkoxycarbonyl groups are then reviewed, followed by mention of those containing Si, N or S in the side-chain and finally polycyclic types with saturated and unsaturated rings bearing hetero atoms. As before emphasis has been placed on developments in the last decade. 

A series of compounds mostly having t-butyl groups, belonging to the group of crypto or hindered phenols and possessing a free 4-position, have been derived by reaction under basic conditions v ith acrylic esters. Thus 2,6-di-tert-butylphenol under basic conditions undergoes Michael addition with methyl acrylate to afford methyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate (ref.53). 

Figure 3.6 shows a chromatogram of a mixture of additives found by chromatography of a mixture of additives, solvent extracted with methyl chloride from a sample of polypropylene (PP). The mobile phase was water (channel A) and acetonitrile (channel B). The analysis performed on a Hewlett Packard Model HP109 Series M LC equipped with a diode array detector, shows the presence of methylated hydroxy toluene, methylated hydroxyethyl benzene. Amide E (erucamide), Irganox 1010 and Irganox 1076 (both sterically hindered phenols). 

Table 4. Effectiveness of a Series of Hindered Phenol Antioxidants ...

The intramolecular process (a) amounts to hindered rotation about the C—0 bond of the phenol. It may be exclusively studied therefore by obtaining accurate chemical shifts at infinite dilution in an inert solvent at a series of temperatures. The equilibrium constant can be written... 

The methylphenols (cresols and the dimethylphenols (xylenols) also respond to alkylation although this procedure is practically exclusively confined to the tert-butyl series. For example, the majority of compounds produced are hindered or crypto phenols the chemistry of which has been discussed in an earlier chapter. For these alkylations a small proportion of sulphuric acid is employed at moderate temperatures. When more valuable alkenes are involved and the objective is the yield of product, boron trifluoride is favoured as a catalyst. 

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