Catalysts take to the bottle: Rhodium amides with a saw‐horse structure serve as very efficient catalysts for the transfer hydrogenation of ketones and activated olefins using ethanol as hydrogen donor. Under mild conditions, the corresponding alcohols and ethyl acetate are formed with high efficiency, with a turnover frequency above 500 000 h−1.
Direct methane functionalization to value-added products remains a challenge because of the propensity for overoxidation in many reaction environments. Sulfonation has emerged as an attractive approach for achieving the necessary selectivity. Here, we report a practical process for the production of methanesulfonic acid (MSA) from only two reactants: methane and sulfur trioxide. We have achieved >99% selectivity and yield of MSA. The electrophilic initiator based on a sulfonyl peroxide derivative is protonated under superacidic conditions, producing a highly electrophilic oxygen atom capable of activating a C–H bond of methane. Mechanistic studies support the formation of CH3+as a key intermediate. This method is readily scalable with reactors connected in series for prospective production of up to 20 metric tons per year of MSA.
Photoinitiators allow the production of polymers and coatings with high control and variety in the process parameters. [1] A broad range of technical applications, unthinkable a few years ago, have now been firmly established. [2] These developments were also driven by the syntheses of new types of photoinitiators. [3] Starting from simple peroxides or a-hydroxy ketones, functionalized oxime esters, [4] organo phosphorus, [1] or, more recently, germanium compounds [5,6] have been developed as highly sophisticated photoinitiators with specific properties. [7,8] Among these, intensively studied mono-acylphosphane oxides (MAPOs, such as Ph 2 PO(COMes), Mes = mesityl; trade name Lucirin TPO) and especially bis-(acyl)phosphane oxides [BAPOs, such as PhPO(COMes) 2 ; trade name IRGACURE 819] stand out owing to their excellent efficiency and activity. [9][10][11][12][13][14][15][16] Irradiation with even a weak light source in the visible range leads to the formation of a phosphinoyl and an acyl radical through a Norrish type I cleavage reaction [Eq. (1)]:BAPOs offer several unique advantages: 1) Photolysis yields a total of up to four radicals, with the phosphinoyl radical about 1000 times more reactive than the acyl radicals. 2) Light in the visible region is absorbed by BAPOs (l = 360-440 nm), but the cleavage products are transparent. This property leads to a high curing depth and allows BAPOs to be applied as initiators, even for relatively thick clear coatings. 3) BAPOs show a relatively high thermal stability (> 100 8C) and can be easily stored. [17,18] Despite their widespread industrial use, very few BAPO derivatives have been synthesized to date. [19] The reported synthetic routes requiring a primary phosphane (RPH 2 ) or a metallated derivative (RPH 2Àx M x ) are incompatible with many functional groups and only aryl or alkyl substituents are bound to the phosphorus atom. Herein, we report a simple method for the synthesis of P-functionalized BAPO derivatives (Scheme 1), which offers interesting possibilities for surface modification.NaPH 2 is easily obtained from elemental phosphorus, sodium, and tert-butanol in the form of a sodium tert-butylate aggregate, which is a versatile starting material for functional phosphorus compounds. [20] Without prior isolation, the aggregate compound NaPH 2 (NaOtBu) x 1 was reacted with mesitoyl chloride to give sodium bis(mesitoyl)phosphide 2 in > 80 % yield as bright yellow crystals (Scheme 1). The structure of 2 (Figure 1) was obtained from a X-ray diffraction study with crystals obtained from a hot toluene/THF mixture (10:1) that contained residual dimethoxyethane (DME). [21] This compound Na 2 [P(COMes) 2 ] 2 ·2 THF·DME, contains two almost planar six-membered NaO 2 C 2 P rings formed by the P(COMes) 2 À anion, which is structurally similar to an acetylacetonate ion, chelating one sodium cation. These rings aggregate to form a strongly folded central Na 2 O 2 ring. Scheme 1. Synthesis of P-functionalized bis(acyl)phosphane oxides (BAPOs). FG = functional group, Mes = mes...
A straightforward high-yield synthesis for the photoinitiator bis(2,4,6-trimethylbenzoyl)phenylphosphane oxide (16, IRGACURE 819) involves: i) the reaction of phenyldichlorophosphane, PhPCl2, with sodium to give [Na2(P2Ph2)(tmeda)]6 (5); ii) protonation of 5 with tert-butanol to give 1,2-diphenyldiphosphane, PhHP-PHPh (12); iii) reduction of 12 by sodium to yield [Na(PHPh)]x (13); iv) protonation of 13 with tert-butanol to give phenylphosphane PhPH2 (14) in excellent yields; v) reaction of 14 with 2,4,6-trimethylbenzoylchloride (MesCOCl) in presence of the NaOt-Bu formed in steps ii and iv to give bis(2,4,6-trimethylbenzoyl)phenylphosphane 7; vi) oxygenation of 7 with 30% aqueous hydrogen peroxide to give the final product 16. This reaction can be performed in toluene with about 4 vol-% of tmeda as an activator in a one-pot synthesis without changing the solvent. The structures determined by X-ray diffraction of the unique hexameric aggregate 5 and 16 are reported.
Trinkfeste Katalysatoren: Rhodiumamidkomplexe mit Sägebockstruktur sind hoch effiziente Katalysatoren für die Transferhydrierung von Ketonen und aktivierten Olefinen mit Ethanol als Wasserstoffdonor. Unter milden Bedingungen entstehen in dieser irreversiblen Reaktion Alkohole und Ethylacetat, und die Umsatzfrequenzen übersteigen teilweise 500 000 h−1.
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