THE SOLVENT CHALLENGE IN SYNTHESIS - THE WORKUP AS EXAMPLE

Pinto, José Ricardo M.; Ribeiro, Maria Gabriela T. C.; Machado, Adélio A. S. C.

doi:10.21577/0100-4042.20170400

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Educação • Quím. Nova 42 (8) • Aug 2019 • https://doi.org/10.21577/0100-4042.20170400 copy

THE SOLVENT CHALLENGE IN SYNTHESIS - THE WORKUP AS EXAMPLE

Authorship SCIMAGO INSTITUTIONS RANKINGS

A procedure for the assessment and optimization of the greenness of solvents in synthesis was developed. It involves two optimization components, aiming at the optimization of both the intrinsic greenness of the solvents and their efficiency to improve the overall green performance of the synthesis, evaluated with mass, energy and time greenness metrics. The procedure was tested in a study with educational purpose for assessing and improving the greenness of solvents used in the workup step of a ionic liquid synthesis that involves a solventless reaction step (1-hexyl-3-methylimidazolium chloride) and proved useful to systematize the aspects that should be considered to choose the solvents used in the workup. The results show that there may be a competition in the solvent choice between a safer solvent and a more hazardous solvent with better performance of the overall synthesis process, which requires optimization for reaching a balanced solution. The study illustrates the problems of the substitution of solvents in synthetic processes to improve greenness, as well as the importance of the utilization of a battery of greenness metrics for evaluation of the overall synthesis outcomes.

Keywords:
green chemistry; green chemistry education; synthesis solvents; greenness improvement; green metrics

Abreviatura	Métrica	Fórmula
AE	Economia atómica	$AE = 100 (\frac{p \cdot {MM}_{P}}{a \cdot {MM}_{A} + b \cdot M M_{B}})$
RME	Eficiência de massa da reação	$RME = 100 (\frac{m_{P}}{m_{A} + m_{B}})$
MI	Intensidade de massa	$MI = \frac{m_{A} + m_{B} + m_{s} + m_{aux}}{m_{P}}$
EI	Intensidade de energia	$EI = \frac{E}{m_{P}} = \frac{E (RS) + E (WS)}{m_{P}}$
TI	Intensidade de tempo	$TI = \frac{t}{m_{P}} = \frac{t (RS) + t (WS)}{m_{P}}$

Abreviatura	Métrica	Fórmula
MI(RS)	MI parcelar para a reação	$MI (RS) = \frac{m_{A} + m_{B} + m_{s} (RS) + m_{aux} (RS)}{m_{P}}$
MI(WS)	MI parcelar para o workup	$MI (WS) = \frac{m_{s} (WS) + m_{aux} (WS)}{m_{P}}$
SI	MI parcelar para os solventes	$SI = \frac{m_{S}}{m_{P}} = \frac{m_{s} (RS) + m_{s} (WS)}{m_{P}}$
ReagI	MI parcelar para os reagentes não solventes	$ReagI = \frac{m_{A} + m_{B} + m_{aux} (RS) + m_{aux} (WS)}{m_{P}}$
EI(RS)	EI parcelar para a reação	$EI (RS) = \frac{E (RS)}{m_{P}}$
EI(WS)	EI parcelar para o workup	$EI (WS) = \frac{E (WS)}{m_{P}}$
TI(RS)	TI parcelar para a reação	$TI (RS) = \frac{t (RS)}{m_{P}}$
TI(WS)	TI parcelar para o workup	$TI (WS) = \frac{t (WS)}{m_{P}}$

Protocolo	B N=1	C N=2	C-B / %
Rendimento / %	84,3	85,0±1,0	0,8
AE / %	100,0	100,0	0,0
RME / %	83,8	84,8±0,8	1,2
MI = ReagI + SI	5,12	6,15±0,06	20,1
SI= SI(WS)	3,92	4,97±0,05	26,8
ReagI = ReagI(RS)	1,19	1,18±0,1	-0,84
EI / Wh g^-1	7,9	9,4±0,4	19
TI / h g^-1	0,171	0,177 ±0,007	-0,6

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