RSC Advances
Paper
a white solid (12.3 mmol, 90%). TLC (DCM/EtOH 8 : 1 v/v): 4-
Experimental
Materials and chemicals
methoxybenzoic acid-d3 Rf ¼ 0.79; FTIR: 3500–2000 (O–H), 1675
(C]O), 1601, 1575, 1513, 1429, 1299, 1270 cmꢁ1 1H NMR
;
(400.13 MHz, DMSO-d6) d ¼ 12.54 (br. s, 1H, COOH), 7.88 (d, J ¼
8.6 Hz, 2H, CarH), 6.99 ppm (d, J ¼ 8.9 Hz, 2H, CarH); 2H NMR
(61.42 MHz, DMSO-d6) d ¼ 3.77 ppm (s, 3D, CD3); 13C NMR
(100.61 MHz, DMSO-d6) d ¼ 167.2 (C]O), 163.0 (Cq–O), 131.5
(CarH), 123.2 (Cq), 114.0 ppm (CarH), n.d. (OCD3); ESI-MS
(8 ppm in MeOH, positive ionization mode): 156.0 m/z ([M +
H]+, C8H6D3O3); melting point: 184–186 ꢀC (water); purity
Ethyl 4-hydroxybenzoate, iodomethane-d3 (99.5 atom% D)
iodoethane-d3 (99.5 atom% D), HI (57%), HCl, acetone, ethyl
acetate, methanol, diethyl ether, sodium hydroxide, potassium
carbonate, magnesium sulfate, and sodium bicarbonate were
obtained from Sigma-Aldrich GmbH (Schnelldorf, Germany).
Indulin AT lignin was from MeadWestvaco (Charlston, SC,
USA). Other technical lignin samples were provided by collab-
oration partners. Lignin samples were puried in accordance
with procedures described in the literature.27,36 Prior to all
analyses, lignin samples were freeze-dried followed by vacuum
1
according to H-NMR: 99%.
Ethyl 4-(ethoxy-d5)-benzoate (3)
ꢀ
oven drying at 40 C until complete dryness.
Ethyl 4-(ethoxy-d5)benzoate was synthesized according to
the procedure described for compound (1). TLC (hexane/
EtOAc 7 : 3): ethyl 4-hydroxybenzoate Rf ¼ 0.43, ethyl 4-
(ethoxy-d5)-benzoate Rf ¼ 0.80; FTIR: 1707 (C]O), 1605, 1508,
Ethyl 4-(methoxy-d3)-benzoate (1)
Ethyl 4-hydroxybenzoate (2.50 g, 15.0 mmol) was dissolved in
dry acetone (50 mL), and K2CO3 (3.22 g, 23.3 mmol) was added
upon constant stirring. CD3I (1.40 mL, 22.5 mmol) was added to
the suspension, and the reaction mixture was allowed to stir for
48 h at RT. The progress of the reaction was controlled by TLC
(hexane/EtOAc 7 : 3 v/v). The white suspension was ltered,
acetone was evaporated, and aer dissolution in CH2Cl2, the
product was washed with saturated aqueous NaHCO3 solution
followed by water until the washings were neutral. Aer
washing with saturated brine, the organic phase was dried over
anhydrous MgSO4, ltered on a sintered glass lter with appli-
cation of a weak vacuum, and evaporated to dryness. The crude
product (transparent oil) was puried by ash column chro-
matography with hexane/EtOAc (7 : 3 v/v) as the isocratic eluent.
Fractions containing the pure product were combined, ltered,
and evaporated to dryness under reduced pressure. The evap-
oration procedure was repeated twice aer the addition of
CHCl3 (app. 10 mL) yield: 2.65 g of transparent oil (14.5 mmol,
97%). TLC (hexane/EtOAc 7 : 3 v/v): ethyl 4-hydroxybenzoate Rf
¼ 0.43, ethyl 4-(methoxy-d3)benzoate Rf ¼ 0.77; FTIR: 2982 (C–
1255, 1167, 1097, 846, 769, 696 cmꢁ1 1H NMR (400.13 MHz,
;
CDCl3) d ¼ 7.99 (dt, J ¼ 8.9, 2.5 Hz, 2H, CarH), 6.90 (dt, J ¼ 8.9,
2.5 Hz, 2H, CarH), 4.35 (q, J ¼ 7.1 Hz, 2H, CH2), 1.38 ppm (t, J ¼
2
7.1 Hz, 3H, CH3); H NMR (61.42 MHz, CDCl3) d ¼ 4.06 (s, 2D,
CD2), 1.39 ppm (s, 3D, CD3); 13C NMR (100.61 MHz, CDCl3) d ¼
166.4 (C]O), 162.7 (Cq–O), 131.5 (CarH), 122.7 (Cq), 114.0
(CarH), 60.6 (CH2), n.d. (CD2), 14.4 ppm (CH3), n.d. (CD3); purity
1
according to H NMR: 98%.
4-(Ethoxy-d5)benzoic acid (4)
4-(Ethoxy-d5)benzoic acid was synthesized according to the
procedure described for compound (2). TLC (DCM/MeOH 5 : 1):
4-(ethoxy-d5)benzoic acid Rf ¼ 0.72; FTIR: 3200–2300 (O–H),
1668 (C]O), 1605, 1432, 1300, 1268, 1175, 1100, 988, 932, 848,
772, 620 cmꢁ1; 1H-NMR (400.13 MHz, DMSO-d6) d ¼ 7.87 (d, J ¼
9.0 Hz, 2H, CarH), 6.97 ppm (d, J ¼ 9.0 Hz, 2H, CarH); 2H-NMR
(61.42 MHz, DMSO-d6) d ¼ 4.04 (s, 2D, CD2), 1.29 ppm (s, 3D,
CD3);13C-NMR (100.61 MHz, DMSO-d6) d ¼ 166.9 (C]O), 162.1
(Cq–O), 131.2 (CarH), 122.7 (Cq), 114.0 ppm (CarH), n.d. (CD2),
H), 1706 (C]O), 1604, 1509, 1257, 1168, 1096, 769 cmꢁ1 1H
;
ꢀ
n.d. (CD3); melting point: 197–199 C (water); purity according
1
NMR (400.13 MHz, CDCl3) d ¼ 8.01 (d, J ¼ 9.0 Hz, 2H, CarH),
6.92 (d, J ¼ 9.0 Hz, 2H, CarH), 4.35 (q, J ¼ 7.2 Hz, 2H, CH2),
1.39 ppm (t, J ¼ 7.2 Hz, 3H, CH3); 2H NMR (61.42 MHz, CDCl3)
d ¼ 3.84 ppm (s, 3D, CD3); 13C NMR (100.61 MHz, CDCl3) d ¼
166.4 (C]O), 163.2 (Cq–O), 131.5 (CarH), 122.9 (Cq), 113.5
(CarH), 60.6 (CH2), 54.6 (sept, J ¼ 21.3 Hz, 3D, OCD3), 14.4 ppm
to H NMR: 99%.
HI acid treatment and sample preparation
Approximately 1 mL of HI acid (57%) was added to a 10 mL
headspace screw cap vial (ND18 magnetic, Bruckner Analy-
sentechnik, Linz, Austria) containing the lignin sample (5–10
mg), internal standards 4-(methoxy-d3)-benzoic acid (4–5 mg)
and 4-(ethoxy-d5)-benzoic acid (2–3 mg), and a small magnetic
stirring bar. The vials were tightly closed with screw caps
1
(CH3); purity according to H NMR: 95%.
4-(Methoxy-d3)-benzoic acid (2)
Ethyl 4-(methoxy-d3)benzoate (2.50 g, 13.7 mmol) was dissolved equipped with PTFE-covered silicon septa (1.3 mm; Bruckner
in MeOH (20 mL), and a solution of NaOH (0.87 g, 21.8 mmol) in Analysentechnik, Linz, Austria) and placed in a heating/stirring
water (20 mL) was added. MeOH was added until complete module (Pierce Reacti-Therm III) for 3 h at 110 ꢀC. Subse-
dissolution of all reagents. The clear solution was stirred for 3 h quently, the vials were cooled to room temperature, and 4 mL of
at reux conditions. The reaction mixture was diluted with cold water were injected through the septa. In experiments on the
ꢀ
distilled water (20 mL), cooled to 0 C, and then acidied with pH-dependent stability of analytes, in which excess HI was
concentrated HCl to approximately a pH of 2. The product partially or completely neutralized, 4 mL of 1.1 or 2.2 M NaOH
immediately precipitated as a white solid. The solid was ltered were injected. Thus, the volume of the liquid phase in all
and washed with cold distilled water until the washings were experiments was adjusted to approximately half of the total vial
neutral. The product was then lyophilized. Yield: 1.91 g of volume. This decreased the phase ratio and, together with
22976 | RSC Adv., 2017, 7, 22974–22982
This journal is © The Royal Society of Chemistry 2017