Scraped/typed into Arcturus
Mat Todd has made some great suggestions about what we can measure in the Green Chain reaction. Here’s his comments on the Etherpad (http://okfnpad.org/solo10 ) and my additions. Please comment and add extra ideas. I’ll show some phrases below and let YOU test your ability. YOU DON’T NEED TO KNOW MUCH CHEMISTRY.
Has there been a shift away from chlorinated solvents in recent years?
PMR Should be easy to find the solvent and classify it/them. The linguistic and contextual pointers to solvents (“3 g of X in Y”, generally identifies Y as a solvent) have been identified by Lezan Hawizy.
Are there more catalytic reactions being carried out now vs 10 years ago?
PMR Catalysts can be identified by
- molar amount. If 1 mmol or A reacts with 1 mmol of B and there is 0.01 mmol of C, then C is almost certainly a catalyst.
actual composition. If a reaction involves zeolites, platinum, or “Wilkinson’s catalyst” then these are likely to be catalysts
- type of reaction. It may be possible to spot the fact that a reaction is catalysed by its type. Thus hydrogenation often requires catalysts.
- Linguistic pointers. The phrases “catalysed by”, “added the catalyst” may be included – though this is often not actually included.
- Similarity with other reactions. This involves full analysis of the reaction language.
What proportion of organic molecules are purified by crystallization (good) vs chromatography (bad).
PMR This Should be relatively easy. The workup phrases are fairly standard and crystallization is usually mentioned explicitly
There are more complex questions concerning atom economy that it would be awesome to look at, but they’re tricky. e.g. what proportion of the atoms put into the reaction end up as part of the product vs things that are byproducts and are thrown away, such as salts, water, gases that you essentially “lose”)
PMR – agreed. Problem here is that it’s tricky to work out the reaction as normally only have reactants and product (singular). Have to manage stoichiometry, etc. But not impossible
Here’s a typical reaction, selected at random (the subscripts come out as <sub>3</sub>, etc.). See if you can answer Mat’s questions – solvent? Catalyst? Crystallization?
<p id=”p0067“ num=”0067“>A 3-neck 300 mL round-bottomed flask equipped with a reflux condenser, magnetic stir bar and a nitrogen inlet was charged with 5 g (1 equivalent) of 4-hydroxybenzonitrile, absolute ethanol 150 mL, and 15.7 mL (1 equivalent) of sodium ethoxide. This mixture was stirred at 25 °C for 15 minutes. Ethyl 8-bromooctanoate (10.5 g, 1 equivalent) was then added dropwise over 10 minutes. The resulting mixture was heated to reflux (75 °C) for 72 hours.</p>
<p id=”p0068“ num=”0068“>
The reaction mixture was cooled and the solids filtered off. The solvent was removed on a rotary evaporator. The crude residue was dissolved in methylene chloride (200 mL) and washed with saturated NaHCO
(2 x 75 mL), H
O (1 x 100 mL) and brine (1 x 100 mL). The crude material was then dissolved in ethanol (125 mL) and water (10 mL). LiOH (5 g) was added and the resulting mixture was heated to reflux (75 °C) for 1 hour then stirred at ambient temperature overnight. The solvent was evaporated and 75 mL of H
O was added. The aqueous solution was acidified to a pH of about 3 with concentrated HCl and the flask cooled to 4 °C. An off-white colored solid precipitated. This material was collected by vacuum filtration and dried on the high vacuum overnight to give the crude acid. These solids were further purified by recrystallization from Ethyl acetate/hexanes (95/5) and again with chloroform to give 4.5 g of the product, 8-(4-cyanophenoxy)octanoic acid (41 % yield).