Synthesis of new trimeric lignin model compounds containing 5-5' and beta-O-4' substructures, and their characterization by 1D and 2D NMR Techniques

Abstract

Os trímeros-modelo de lignina contendo as subestruturas bifenila (5-5') e aril-éter (β-O-4') foram sintetizados a partir dos derivados da desidrodivanilina e da α-bromo acetovanilona pela reação de Williamson. O estudo de RMN de 1 H e de 13 C destes trímeros foi feito utilizando as técnicas homo e heteronucleares. A atribuição dos sinais de RMN de 1 H e de 13 C e a conformação das moléculas são também discutidas neste artigo.Trimeric lignin model compounds containing biphenyl (5-5') and β-aryl ether (β-O-4') were synthesized from dehydrodivanillin derivatives and α-bromo acetovanillone derivatives via Williamson's reaction. The 1 H and 13 C NMR characteristics of the resulting trimers were studied using corresponding 1 H and 13 C NMR spectra as well as homo-and heteronuclear 2D NMR techniques. The results are discussed in terms of signal assignment and conformation of the molecules.

Comparative Studies on the Delignification of Pine Kraft−Anthraquinone Pulp with Hydrogen Peroxide by Binucleus Mn(IV) Complex Catalysis

“…The lignin also contained a biphenyl (5-5) structure (4), a stilbene structure (5), and 5-5 structures with an R-carbonyl and/or an R-carboxylic acid group (7). The very intensive cross-signal centered at δ C /δ H 120.5/6.68 corresponded to CH-6/CH-6′ of 4, whereas cross-signals at δ C /δ H 112.2/7.53 and 126.2/7.59 corresponded CH-2 and CH-6 of etherifed 7 (L 1 ) lignin moiety), respectively (27)(28)(29). In addition, the intensive cross-signals at δ C /δ H 120.6/7.26 and 128.5/7.2-7.4 corresponded to CH-6 and the conjugated -CHdCHgroup of 5, respectively (27).…”

Reaction Mechanisms in Delignification of Pine Kraft-AQ Pulp with Hydrogen Peroxide Using Mn(IV)-Me4DTNE as Catalyst

“…Moreover, an anti-Markovnikov addition of hydroperoxide anion (HOO -) on C-R gives R-hydroperoxyl-β-hydroxyl intermediate 5d that undergoes cleavage of the C R -C β bond, resulting in degradation of 5d into aryl aldehyde fragments 5e and 5f. Hege et al 22 showed that epoxidation reactions with H 2 18 O 2 using a similar catalyst result in producing the corresponding epoxides that contained 100% 18 O. This suggests that H 2 O 2 is the source of oxygen, not water, which is in agreement with the proposed reaction mechanism, besides the model compound experiments.…”

“…Furthermore, the aromatic region of the HMQC spectrum of KRL ( Figure B ) shows that the KRL also contains biphenyl (5−5) structure ( 4 ), stilbene structure ( 5 ), and also 5−5 structures with a α-carbonyl and/or α-carboxylic acid group ( 7 ). The cross-signal centered at δ C /δ H 120.6/6.68 corresponds to CH-6/CH-6‘ of 4 , while those at δ C /δ H 112.2/7.53 and δ C /δ H range of 126.3−127.0/7.44−7.60 correspond to CH-2 and CH-6 of etherified 7 , respectively ( − ). The signals at δ C /δ H 120.3/7.26 and 128.4/7.32 correspond to CH-6 and -CHCH- groups in 5 , respectively ().…”

Radical synthesis of tetrameric lignin model compound

“…Although the synthesis of trimmers [4] The activation of potassium persulfate promoted by ferrous 77 sulfate to generate sulfate radical is commonly carried out in 78 aqueous media [9]. However, the addition of acetone increases the (Table 1), which shows that a higher 80 yield is obtained when the volume ratio of acetone to water is 2:1.…”