128 Introduction to Renewable Biomaterials
Internal standard
(a)
(b)
(c)
Lignin-OH + CI P Lignin-O + HCI
O CDCI 3
O Pyridine
P
O
O
Aliphatic OH
155 150 145 140 135 ppm
C 5 substituted
COOH
Guaiacyl
OH
TMDP
hydrolysis
product
O
O
OCH 3 H 3 CO OCH 3 OCH 3
O
P
O
O
O
P
O
O
O
P
O
O
O
P O
O
R O
Aliphatic-OH
Guaiacyl Syringyl p-Hydroxyphenyl C 5 substituted Carboxylic
O
P
O
O
RO P
p-Hydroxy
phenyl
Figure 4.6Phosphorylation of lignin with 2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane
(TMDP) is fast and reaction products (c) are shown in^31 P NMR spectrum (b) and lignin modified (a).
examining the breakdown products. Figure 4.6b shows an example of the^31 PNMR
spectrum of a softwood lignin derivatized with TMDP using HNDI as internal standard
[107]. Typical chemical shift ranges and spectral regions for integration are shown in
Table 4.4.
4.11.3 2D HSQC
2D^1 H–^13 C solution-state NMR spectroscopy has been developed to reveal detailed
information about lignin structure. This technique offers a semiquantitative analysis
of lignin structure of ball-milled lignocellulose without extraction and acetylation of
lignin. Dimethyl sulfoxide-d 6 is commonly used as a lock solvent during the proce-
dure. In some cases, a minute amount of co-solvent, such as 1-methylimidazole (or
N-methylimidazole) [48], pyridine [4, 45], and 1-ethyl-3-methyl-imidazolium acetate
[27, 46], can be added to aid lignocellulose solubility, increasing solution viscosity
and in turn decreasing the relaxation time. Figure 4.7a, b, and c shows the 2D HSQC
