Polyethylene Glycols as Efficient Catalysts for the Oxidation of Xanthine Alkaloids by Ceric Ammonium Nitrate in Acetonitrile: A Kinetic and Mechanistic Approach

Table 2

Activation parameters of caffeine in different PEG media.

Type of PEG	PEG % (V/V)	𝑘^′′ at 300 K	Equation obtained for plot of; ln(𝑘^′′/𝑇) versus (10^3/𝑇)	𝑅^2	Δ𝐻^#	Δ𝐺^#	−Δ𝑆^# J/Kmol
					kJ/mol
PEG-200	0.5	0.4	𝑦=−4.1044𝑥+7.088	0.985	34.1	75.2	138
	1.0	0.5	𝑦=−3.9118𝑥+6.686	0.963	32.4	74.7	141
	2.0	0.6	𝑦=−3.4191𝑥+5.218	0.968	28.3	74.5	154
	3.0	0.6	𝑦=−5.24𝑥+11.28	0.989	43.5	74.7	103
	4.0	0.7	𝑦=−4.4927𝑥+8.922	0.999	37.2	74.2	123
	5.0	0.9	𝑦=−3.9922𝑥+7.503	0.999	33.1	73.6	135
PEG-300	0.5	0.2	𝑦=−5.7209𝑥+11.77	0.997	47.5	76.6	99.7
	1.0	0.3	𝑦=−4.4045𝑥+7.775	1.00	36.5	76.1	132
	2.0	0.4	𝑦=−4.1044𝑥+7.088	0.986	34.1	75.5	138
	3.0	0.5	𝑦=−3.0174𝑥+3.654	0.998	25.0	75.1	167
	4.0	0.6	𝑦=−2.1466𝑥+0.948	0.995	17.8	74.5	189
	5.0	0.7	𝑦=−1.8624𝑥+0.153	0.996	15.4	73.5	196
PEG-400	0.5	0.2	𝑦=−4.0901𝑥+6.298	0.992	33.9	75.6	139
	1.0	0.4	𝑦=−1.6439𝑥−1.125	0.974	13.6	70.0	188
	2.0	0.5	𝑦=−1.3085𝑥−2.031	0.998	10.8	64.8	180
	3.0	0.6	𝑦=−1.0727𝑥−2.636	0.999	8.90	61.4	175
	4.0	0.7	𝑦=−3.0329𝑥+4.079	0.971	25.1	74.0	163
	5.0	0.8	𝑦=−3.0238𝑥+4.168	0.992	25.0	73.6	162
PEG-600	0.5	0.2	𝑦=−4.9831𝑥+9.337	0.980	41.3	77.0	119
	1.0	0.3	𝑦=−3.7714𝑥+5.687	0.988	31.3	76.3	150
	2.0	0.4	𝑦=−3.0286𝑥+3.490	0.992	25.1	75.5	168
	3.0	0.6	𝑦=−1.6344𝑥−0.784	0.966	13.5	70.8	191
	4.0	0.7	𝑦=−1.3993𝑥−1.412	0.963	11.6	67.1	185
	5.0	0.9	𝑦=−0.6541𝑥−3.627	0.999	5.42	55.5	167