The Relationship between Chemical Shift of Carbons on Benzene Ring of Phenols in Aqueous Alkaline Solution and Reaction Activity
Yu Shangxian Yang Jinrui Gu Jiangnan
(College of chemistry, Beijing normal university, Beijing 100875)
A series of research on the relationship between chemical shift of carbons on benzene ring of phenols in neutral or acid solution and electrophilic substitution reaction or nucleophilic addition reaction has been carried out by our group[1,2,3]. The research showed that the chemical shift of carbons on benzene ring of phenols is lower, the reaction activity is higher. The reaction activity of para position carbons is higher than that of ortho position carbons obviously, although the chemical shift of ortho position carbons is lower, which described as “para position priority”. Reaction of phenols and formaldehyde in aqueous alkaline solution is involved when synthesize resol and novolac by stepwise base-acid catalyzed reaction. So, it is necessary to know the chemical shift of carbons on benzene ring of phenols in aqueous alkaline solution. However, systematic studies in this aspect have not yet been reported, and chemical shift can not be found in Sadtler Standard Carbon-13 NMR Spectra.
DEPT135 spectra of phenols were recorded in 1w% aqueous alkaline solution by Avance 500 Bruker NMR (Bruker A. G.) and the mole number of hydroxyl of phenols equals to that of sodium hydroxide. Phenols are industrial grade except xylenol, xylenol and other reagents are analytically pure. Data of chemical shift of carbons on benzene ring of phenols in neutral solution were cited from handbook. Comparison of data in Tab. 1 indicates that chemical shift of carbons on benzene ring of phenols is very different when in aqueous alkaline solution, because hydroxyl group changes into negative oxygen ion in aqueous alkaline solution. Assignment of the signals in DEPT135 spectra can be completed easily, because –CH– and –CH3– are positive peaks, –CH2– is negative peak and –C– doesn’t have response signal. Moreover, the integral value of the peaks is direct proportion to the number of benzene ring carbons. Chemical shift of ortho position carbon is lower than that of para position carbon in neutral solution, but chemical shift of para position carbon is lower than that of ortho position in aqueous alkaline solution. Chemical shift of meta position is highest under two conditions and almost the same. Otherwise, chemical shift of para position carbon decreases when the phenol has one ortho position methyl and the value decreases obviously when has two ortho position methyls.
H/D exchange reaction of some phenols with high reaction activity can lead to difficulty in measurement. However,it can not influence assignment of signals. Assignment of the signals of phenols in DEPT135 spectra can be completed easily in most condition except m-cresol. Chemical shift of carbons on benzene ring of m-cresol can be indicated according to the following discussion. Chemical shift of phenol and p-cresol shows that chemical shift of ortho position carbons increases obviously in aqueous alkaline solution, but the value of para position carbons decreases significantly in aqueous alkaline solution. 2,6-xylenol and 3,5-xylenol show the same effect. Therefore, chemical shift of 2, 4 and 6 position carbons of m-cresol can be assigned as Tab. 1. Perhaps, the data should be interchange between 4 and 6 position carbons. After all, the two data is very close. Whether or no, chemical shift of para position carbon is lower than that of ortho position carbon.
According to document and our research, when temperature is not very high, chemical shift of carbons on benzene ring is lower, the hydroxymethylation carrys out easier in basic condition. In additional, the production is stable in neutral condition[4,5]. These data and conclusion have some guiding significance for synthesis of novolac. We have synthesized o-cresol novolac or mixed-phenol novolac containing mainly o-cresol by base-acid catalyzed reaction, both of which have high Mw and low Mw/Mn. The difficult problem existed more than 100 years in novolac resin field has been solved successfully[6].
Tab. 1 Chemical shifts of carbons on benzene ring of phenols in alkaline aqueous solution or in neutral solution (values in bracket)
phenols |
Chemical shifts of carbons on benzene ring |
2 |
3 |
4 |
5 |
6 |
phenol |
118.8(115.6) |
129.8(129.8) |
114.5(121.1) |
129.8(129.8) |
118.8(115.6) |
resorcinol |
108.4(102.8) |
/ |
106.3(106.7) |
129.6(129.8) |
106.3(106.7) |
catechol |
/ |
116.8(115.8) |
116.4(120.1) |
116.4(120.1) |
116.8(115.8) |
hydroquinone |
118.6(117.2) |
118.6(117.2) |
/ |
118.6(117.2) |
118.6(117.2) |
pyrogallol |
/ |
/ |
106.3(109.4) |
119.3(121.5) |
106.3(109.4) |
phloroglucinol |
98.4(95.2) |
/ |
98.4(95.2) |
/ |
98.4(95.2) |
o-cresol |
/ |
130.4(131.2) |
114.1(121.1) |
127.2(127.1) |
118.1(115.2) |
m-cresol |
119.4(116.4) |
/ |
115.2(122.0) |
129.7(129.6) |
115.8(112.6) |
p-cresol |
118.6(115.6) |
130.1(130.2) |
/ |
130.1(130.2) |
118.6(115.6) |
2,3-xylenol |
/ |
/ |
115.7(122.5) |
126.2(125.9) |
115.9(112.9) |
2,4-xylenol |
/ |
131.0(131.9) |
/ |
127.3(127.5) |
118.0(115.3) |
2,5-xylenol |
/ |
130.3(130.9) |
114.7(121.6) |
/ |
118.8(115.9) |
2,6-xylenol |
/ |
128.1(128.7) |
113.4(123.5) |
128.1(128.7) |
/ |
3,4-xylenol |
119.9(117.0) |
/ |
/ |
130.5(130.5) |
115.6(112.9) |
3,5-xylenol |
116.3(113.3) |
/ |
116.0(122.7) |
/ |
116.3(113.3) |
Reference
1 Gu, J N, Tong X, Zou, Y Q, et al. Proceedings of SPIE-The International Society for Optical Engineering (1999), 3678(Pt.1, Advances in Resist Technology and Processing XVI), 440-447.
2 Yu, Sh X, Tong, X, Wang, L Y, et al. Journal of Beijing normal university(natural science ) (2000), 36(2), 245-249.
3 Yu Sh X, Yang J R, Gu J N. Thermosetting resin, 2006,21(2)5-9.
4 Yang J R, Yu Sh X, Gu J N. Polymer materials science and engineering. 2008,24(1),124-127
5 Yu Sh X, Yang J R. Thermosetting resin,2007,22(2),11-15
6 Yang J R., Cong P J, Shao Y Zh, et al. Thermosetting resin,2009,24(6)1-4.
强碱水溶液中酚类化合物碳原子化学
位移与反应活性的关系
余尚先 杨金瑞 顾江楠
(北京师范大学 化学学院 北京 100875)
测定了合成酚醛树脂时常用酚类化合物在强碱水溶液中的NMR-13C谱,发现所述酚类化合物酚羟基邻、对位苯环碳原子化学位移明显降低,且对位低于邻位。即碱性条件下,活性点碳原子化学位移越低,越容易发生羟甲基化反应,强碱水溶液中苯环碳原子化学位移可作为判断酚类化合物亲电反应的依据。根据这一规律,利用碱酸分步催化的方法,合成了一系列MW高、MW/MN小的邻甲酚系线型酚醛树脂,解决了酚醛树脂合成史上近百年来一直未解决的一大难题。