Manganese Complexes as Drying Catalysts for Alkyd Paints

Common alkyd paint will not have dried within two hours without drying catalysts. The drying catalyst (also called __drier__) that is generally used is based on the heavy metal cobalt. Since cobalt salts are suspected to be carcinogenic, it is of the utmost importance that alternative driers are found and that cobalt can be replaced as a drier in alkyd paint. In this thesis newly developed manganese compounds are presented which show a comparable or better drying activity than existing cobalt driers. These manganese driers are thus potential replacements for the toxic cobalt compounds. Results pertaining to the mechanism of action of the new manganese driers are also discussed. These results will make the future development of alkyd paint driers easier. Huis-tuin-en-keuken alkydverf is uit zichzelf niet binnen twee uur droog. Daarom worden drogingsversnellers (katalysatoren) aan de verf toegevoegd, om het drogingsproces te versnellen. De meest gebruikte drogingskatalysator (ook wel __droger__ genoemd) in alkydverf is gebaseerd op het zware metaal kobalt. Aangezien kobalt vermeend carcinogeen is, is het noodzaak om alternatieve drogers te vinden zodat kobalt vervangen kan worden. In dit proefschrift worden (nieuw ontwikkelde) mangaanverbindingen gepresenteerd die dezelfde of soms zelfs een betere drogingsactiviteit vertonen als de bestaande kobaltdroger en dus als mogelijke vervanger aangemerkt kunnen worden. Ook worden resultaten gepresenteerd mbt de precieze werking van de mangaandrogers, zodat het in de toekomst makkelijker zal zijn nieuwe drogers te ontwikkelen voor bijvoorbeeld een specifieke verfformulering.The work described in this thesis was financially supported by the Dutch Ministry of Economic Affairs, as part of the SENTER/Innovation Oriented Research Program on Heavy Metals (IOP) No. IZW99241c.UBL - phd migration 201

p-type delta-doped layers in silicon: structural and electronic properties

We report on the properties of p-type delta-doped layers prepared in molecular beam epitaxy-Si by growth interruption and evaporation of elemental B. Secondary-ion mass spectrometry measurements at several primary ion energies have been used to show that the full width at half maximum is ~2 nm. Hall measurements confirm that the layers are completely activated at 300 K with a mobility of 30±5 cm2/V s for a carrier density of (9±2)×1012 cm−2. At temperatures below 70 K nonmetallic behavior is observed which we have attributed to conduction between impurity states. It is concluded that the critical acceptor separation for the Mott metal-insulator transition in this system is significantly less than the value found in uniformly doped Si:B

Manganese Complexes as Drying Catalysts for Alkyd Paints

Common alkyd paint will not have dried within two hours without drying catalysts. The drying catalyst (also called __drier__) that is generally used is based on the heavy metal cobalt. Since cobalt salts are suspected to be carcinogenic, it is of the utmost importance that alternative driers are found and that cobalt can be replaced as a drier in alkyd paint. In this thesis newly developed manganese compounds are presented which show a comparable or better drying activity than existing cobalt driers. These manganese driers are thus potential replacements for the toxic cobalt compounds. Results pertaining to the mechanism of action of the new manganese driers are also discussed. These results will make the future development of alkyd paint driers easier. Huis-tuin-en-keuken alkydverf is uit zichzelf niet binnen twee uur droog. Daarom worden drogingsversnellers (katalysatoren) aan de verf toegevoegd, om het drogingsproces te versnellen. De meest gebruikte drogingskatalysator (ook wel __droger__ genoemd) in alkydverf is gebaseerd op het zware metaal kobalt. Aangezien kobalt vermeend carcinogeen is, is het noodzaak om alternatieve drogers te vinden zodat kobalt vervangen kan worden. In dit proefschrift worden (nieuw ontwikkelde) mangaanverbindingen gepresenteerd die dezelfde of soms zelfs een betere drogingsactiviteit vertonen als de bestaande kobaltdroger en dus als mogelijke vervanger aangemerkt kunnen worden. Ook worden resultaten gepresenteerd mbt de precieze werking van de mangaandrogers, zodat het in de toekomst makkelijker zal zijn nieuwe drogers te ontwikkelen voor bijvoorbeeld een specifieke verfformulering

Effect of [Mn(acac)3] and its combination with 2,2'-bipyridine on the autoxidation and oligomerisation of ethyl linoleate

In this study we investigated the autoxidation and oligomerisation of ethyl linoleate (EL) catalysed by [Mn(III)(acac)3] (acac=2,4-pentanedionate) and its combination with 2,2-bipyridine (bpy), in comparison with the EL catalysed by Co(II) 2-ethylhexanoate (Co-EH). EL is a model compound for the alkyd resin in alkyd paints, Co-EH is a common drying catalyst for alkyd paints, and [Mn(acac)3] and the [Mn(acac)3]/bpy combination are potential new drying catalysts. The autoxidation of EL was studied through time-resolved Raman spectroscopy, oxygen uptake measurements, and peroxide amount determination. To follow the oligomerisation of EL in time, size exclusion chromatography was used. Head-space GC-MS measurements were performed to determine the amounts of hexanal and pentanal that were formed as volatile byproducts during the autoxidation of EL. The autoxidation rates of EL in the presence of Co-EH and [Mn(acac)3]/bpy were found to be similar, while the rate in the presence of [Mn(acac)3] was slower. The extent of EL oligomerisation was much higher for [Mn(acac)3] compared to the other catalysts. Different mechanisms are proposed for the mode of action for each of the catalysts: Co-EH is primarily a hydroperoxide decomposition catalyst, as is [Mn(acac)3], only less active. The [Mn(acac)3]/bpy combination probably forms the very reactive complexes [Mn(III)(acac)2(bpy)]+ and [Mn(II)(acac)2(bpy)], which are responsible for a very high autoxidation rate, but also for significant degradation of the formed EL oligomers via â-scission reactions due to the promotion of alkoxy radical formation

The autoxidation activity of new mixed-ligand manganese and iron complexes with tripodal ligands

The activity of new manganese and iron complexes of dianionic tripodal ligands in the autoxidation of ethyl linoleate (EL) is reported. EL consumption rates were monitored using time-resolved FTIR and the degree of oligomerisation was determined by SEC. Almost all complexes showed the same trend in the autoxidation of EL. After a short induction time, the reaction started at a relatively high constant rate; later, this rate changes to a lower rate, which was again constant and on average was the same for all complexes studied. The observation that the autoxidation rate eventually became the same for all complexes can be explained with the assumption that a catalytic species was formed that was structurally similar for each complex. The crystal structure of a representative new complex, [Mn(papy)(acac)] (H2papy = N-(2-hydroxybenzyl)-N-(2-picolyl)-glycine; Hacac = acetylacetone), was elucidated, demonstrating a Jahn–Teller distorted octahedral geometry of the Mn(III) ion. To gain insight into the reaction mechanisms by which these manganese complexes react with peroxides, the reaction of [Mn(pppy)(dpm)] with alkyl hydroperoxides was studied using UV–vis and EPR spectroscopy (H2pppy = 2-[bis(2-hydroxybenzyl)aminomethyl]-pyridine; Hdpm = dipivaloylmethane). It is proposed that in a reaction of [Mn(pppy)(dpm)] with t-butyl hydroperoxide (tBuOOH), the species [Mn(III)(pppy)(OH)(tBuOO•)] is formed. In analogy with the formation of that species, which is postulated to occur through a reduction to Mn(II), it is proposed that in the direct initiation reaction of EL with a manganese(III) complex, a 1 electron–1 proton transfer reaction leads to the formation of Mn(II) and an EL radical. Considering parameters such as autoxidation activity, complex solubility and ease of complex preparation, the compound [Mn(III)(tbpppy)(dpm)] (H2tbpppy = 2-[bis(2-hydroxy-3,5-di-tert-butylbenzyl) aminomethyl]pyridine) is expected to be the best potential alkyd paint drier