Acetyl acetonates, transition metal

A number of metal chelates containing transition metals in their higher oxidation states are known to decompose by one electron transfer process to generate free radical species, which may initiate graft copolymerization reactions. Different transition metals, such as Zn, Fe, V, Co, Cr, Al, etc., have been used in the preparation of metal acetyl acetonates and other diketonates. Several studies demonstrated earlier that metal acetyl acetonates can be used as initiators for vinyl polymeriza-... 

Table 1 lists as examples the chelation characteristics for the transition metal ions with poly(methacroyl acetone) (PMA), poly(vinylacetonyl ketone) (PVAK), acetyl-... 

The suggestion that some uv stabilisers may function by deactivating photo-excited states of molecules, particularly of triplet carbonyl and singlet oxygen, arose largely as a result of fundamental photochemical studies in model systems and many attempts have been made to invoke this mechanism to explain the activity of a variety of photo-stabilisers (13-20). Many effective uv stabilisers are indeed efficient quenchers of photo-excited states (20), but so are many more which are not and in some cases notably the transition metal acetyl acetonates (VI), (28) quenchers of triplet carbonyl are among the most powerful photo-activators known (22). 

Acetyl acetone is used as a reagent for organic synthesis and as a transition metal chelating agent. Its organometallic complexes are used as additives for gasoline and lubricants, and in varnishes, color, ink, and fungicides. 

As a final generalization, it should be mentioned that these radical chain processes are common when transition metal compounds other than phosphine complexes are used. Catalytic oxidations have been carried out with a wide range of metal complexes, and a comparison has been observed between reactions catalyzed by phosphine complexes and those with acetyl-acetonate or other ligands. 

Transition metal ions by themselves, for example in the form of stearates or acetyl acetonates (I), have also been widely used to catalyse the photooxidation of polyolefins. Whilst they are very effective in this respect, they again cause degradation during processing and storage unless used with a metal restraining agent [32, 33] (see below). 

PO can be made degradable by means of additives. The types of additives include aromatic ketones (benzo-phenone and substituted benzophenones [47], qui-none), aromatic amines (trisphenylamine), polycyclic aromatic hydrocarbons (anthracene, certain dyes such as xanthene dyes), or transition metal organic compounds. The transition metal compounds of Fe, Co, Ni, Cr, Mn are widely used. Organo-soluble acetyl acetonates of many transition metals are photooxidants and transition metal carboxylates are also thermal pro-oxidants. Co acetylacetonate appears to be an effective catalyst for chemical degradation of PP in the marine environment. The preferred photoactivator system is ferric dibutyldithiocarbamate with a concentration range of 0.01. 1%. Scott has patented the use of organometallic compounds hke iron (ferric) dibutyldithiocarbamate or Ni-dibutyl-dithiocarbamate [48]. Cerium carboxylate [49] and carbon black are also used in such materials [50]. 

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