MICROWAVES APPLICATION IN ORGANIC SYNTHESIS. Microwave-Assisted Preparation of Diphenylamines in 'Dry Media'
http://www.unibas.ch/mdpi/ecsoc/a0031.htm
Introduction
In the past few years there has been a growing attention in the use of microwave heating in organic synthesis since the first contributions by Gedye [1] and Giguere [2] in 1986.
Microwave-assisted organic synthesis have several advantages over conventional technology: remarkable decreases in the times necessary to carry out reactions (up to 3 orders of magnitude), improved isolated yields of products (when thermal decomposition is associated with the conventionally heated reactions) and, sometimes effects on chemo-, regio- and stereoselectivity, are also achieved. On the other hand, it was shown that microwaves have a specific catalytic effect, named ³microwave effect², lowering the activation energy of a reaction [3]. Other investigators have observed similar microwave effects (i.e. reduced processing temperatures and times) in glasses and polymers, and these results have created much interest and controversy in the microwave processing community [4]. At present, there is a little doubt that measured processing temperatures and times are reduced when conventional heating is replaced with microwave energy. At issue are the underlying causes/mechanisms responsible for this effect. Specifically, is there a nonthermal effect, or are the measured temperatures not representative of the true temperatures due to inaccuracies in the temperature probe or the presence of temperature gradients? As we mentioned above, the issue of microwave effects is very controversial. Unfortunately, many of the expected results from microwave processing such as rapid and uniform heating, inverse temperature profiles, and selective heating are included in the general microwave effects [5]. However, it is affirmed that only those anomalies that cannot be predicted or easily explained based on our present understanding between thermal and microwave heating should be called ³microwave effects² [6]. Enhancements in the rates of activated processes involving material transport (i.e. sintering, ion exchange, and chemical reactions) are considered microwave effects because a reduction in the activation energy appears to be required, and investigators have been unable to provide a scientific basis for this behavior. In addition to enhanced rates, differences in reaction pathways and reaction products due to microwave processing also should be considered microwave effects [7]. Enhanced rates have been attributed to poor temperature measurements in a microwave field and localized temperature variations. To date, neither has been proven to be responsible for the observed enhancements. Many of the investigations reporting enhancements in processing rates and lower processing temperatures have paid close attention to temperature measurements; sheathed thermocuples, optical fibers [8] and non-contact measurements devices have been used. However, accurate temperature measurements are difficult in the presence of thermal gradients, which most certainly occur during microwave processing of bulk samples. Therefore, more emphasis should be placed on reporting the method of temperature measurement, the accuracy, and where the measurements are made (i.e. on the sample surface or in the interior). The simplest method for conducting microwave-assisted reactions involves irradiation of reactants only, in an open container made from quartz, Teflon or ceramic material. The scope for such processes is obviously limited, because of the reduced number of suitable organic compounds. Consequently, two other solvent-free techniques have been developed: reactions on solid mineral support in Œdry media¹, and solid-liquid phase transfer catalysis. For Œdry media¹ reactions, supports such as alumina, silica, bentonite, montmorillonite clays, and zeolites, have been investigated. Although this technique seems best suited to transformations involving a single organic species (e.g. as in deprotection, rearrangement, oxidation and dehydration), condensations have also been reported [9].
it's just mediocre in it's relevance, but anywho.
M_G, Dare ya to try it!
Calcium hydroxide thermally decomposed to calcium oxide and water using a microwave assisted dry (not for long hopefully)-media.
I will try it if you don't want to, or GOD you try it since you want it. Wouldn't it bee fun? yes
A ceramic dish, covered(?) with pierced microwavable plastic wrap. Zap it for a few seconds...Take it out of your mommas oven, if it appears wet, then goodie, try for 5seconds!
Wait for one of the red guys to say its alright.
