Chemistry Reference
In-Depth Information
Cooler
Essential oil
Aqueous phase
System of water reflux
Microwave oven
Reactor
Plant material
Figure 3.7
Apparatus for solvent free microwave assisted extraction. Reproduced from [19] with permission
from Elsevier, © 2004.
(
Thymus vulgaris L.
). The essential oils extracted by SFME for 30 min were similar in yield and in their
aromatic profiles to those obtained by conventional hydrodistillation for 4.5 h. The SFME method yields an
essential oil with higher amounts of more valuable oxygenated compounds, and saves cost, time, energy and
plant material. SFME is a green technology and appears as a better alternative for the extraction of essential
oils from aromatic plants.
3.2.3
Green alternatives for chemical reactions
Several strategies can be adopted aiming greener analytical procedures, involving replacement of toxic
reagents, minimization of reagent consumption, recycling and waste treatment. However, the development
should be carried out without critically affecting key analytical features such as sensitively, accuracy and
precision. This challenge becomes more serious for analytes in low concentration, especially in samples with
complex matrices [20]. For this reason, laboratory experiments with an environmentally friendly orientation
have emerged covering a wide variety of issues concerning chemical reactions. Following discussion is
focused on an overview of some well known greener chemical reactions for analytical laboratory.
3.2.3.1
The green chemical approach for nitration of aromatic compounds
In several industrially important processes like nitration of aromatic compounds, a large excess of sulfuric acid
is required because the by-product water slows down the reaction by diluting the acid [21]. At the end of these
processes, a large amount of 'spent acid' is obtained which, in batch reactions, is usually neutralized and
disposed off, while in continuous processes, it has to be cycled by complex methodologies. Also, the separation
