Carbonyl Group

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Diatomaceous Earth is the fossil remains of plankton that died in the oceans millions of years ago and sank to the bottom to form deposits. Chemically it is predominantly silica which is one of the most abundant elements in the earth.

Filtration using Celite diatomite is a two step operation. First, a thin protective layer of filter aid, called the precoat, is built up on the filter septum by recirculating a filter aid slurry. After precoating, small amounts of filter aid (body feed) are regularly added to the liquid to be filtered. As filtering progresses, the filter aid, mixed with the suspended solids from the unfiltered liquid, is deposited on the precoat. Thus, a new filtering surface is continuously formed. The minute filter aid particles provide countless microscopic channels which entrap suspended impurities but allow liquid to pass through, without clogging.

The first step in the use of Celite is to build up a "precoat" of Celite filter aid on the filter septum. The purpose of the precoat is threefold:

1. To prevent the filter septum from becoming clogged by impurities, thus prolonging septum life.

2. To give immediate clarity.

3. To facilitate cleaning of the septum at the end of the cycle.

Precoating is accomplished by circulating a slurry of filter aid and filtered or clear liquid between the filter and the precoat tank. Since most of the filter aid particles are smaller than the openings in the septum, they must form the precoat by bridging these openings. These bridges can be upset by air bubbles, sudden changes in pressure, or vibrations, causing the filtrate to become turbid until the upsetting influences have been corrected. If flow distribution in the filter is good, the filter may be filled with clear precoat liquid and a concentrated slurry of filter aid may then be pumped or educted into the filter followed by recirculation.

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How Filteraid Works

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After filtering, the residue was washed with water to remove the impurities.

NaCl was added to the filtrate to decrease the solubility of the product. The filtrate was light brown with white solids.

Ethyl acetoacetate was used to extract the product. On the first and extraction, the organic layer which contains the product is a colorless solution with emulsion. The resulting aqueous layer was a yellow mixture. However on the third extraction, the organic layer turned into a colorless solution with a minimum emulsion.

After collecting the organic layers, the combined layers were dried using Na2SO4 until the drying agent stopped to clump together. The solution was decanted and the decantate was distilled. The distillate which contained the desired product was a colorless solution while the pot residue was a yellowish solution.

The yield of the experiment was 49.1%. The percent error of the experiment is 50.9% which can mainly be attributed to the first two extractions wherein the emulsion comprised the main portion of the organic layer. Emulsion can be prevented through repeating the filtration process to remove the excess yeast which contains emulsifiers that can readily interfere in the reaction mixture. Also, emulsion can be prevented through breaking the emulsion through the use of stirring rod. Addition of saturated NaCl to decrease the solubility of the product may also be employed.

In the experiment, two chemical characterization tests were done. The first is the reaction of the starting material and the product with hot KMnO4. Ethyl acetoacetate gave a positive sign of reaction while (S)-ethyl 3-hydroxybutanoate gave a negative result to the test.

In jones test, both the compounds gave a positive result. However, theoretically, the starting material which is not an alcohol should give a negative result. This error may be attributed to the contamination of the reagent which interferes with the result of the jones test.

Other techniques may be employed to test the efficiency of the synthesis of (S)-ethyl 3-hydroxybutanoate by asymmetric induction. Some of these techniques are the Thin layer Chromatography, and the Infrared Spectroscopy. TLC can determine if there is excess ethyl acetoacetate through the spots that can be observed in the chromatogram. Another technique is the Infrared Spectroscopy which can determine if there the presence of hydroxyl group which gives peaks at 3400-3600 and can show unreduced ketones at peaks 1670.

Aside from the chemical tests conducted, physical characterization tests were also performed in the samples. These tests are the determination of the boiling points of the substances and the determination of the optical purity or enantiomeric excess of the samples.

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What does it mean if the enantiomeric excess of a reaction is 30%? Will it be useful to have an enantiomeric excess of 50%? Show important calculations.

(insert calculations)

Outline a scheme for the preparation of (R)-3-hydroxybutanoic acid from ethyl acetate. (Hint: A Claisen condensation is useful)

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In the Asymmetric synthesis of (S)-ethyl-4-chloro-3-hydroxybutanoate using Candida parapsilosis, different parameters were observed: effect of -substrate (glucose) concentration on the asymmetric reduction of COBE, effect of resting cell concentration on the asymmetric reduction, effect of pH on the asymmetric reduction of COBE, and effect of substrate concentration and substrate feeding on the asymmetric reduction.

in the Effect of co-substrate (glucose) concentration on the asymmetric reduction of COBE, it was found that addition of glucose increased its rate of asymmetric reduction. At a concentration of 50 g/l, glucose showed a maximum asymmetric reduction rate of 43.4 § 2 mmol/lh with 100% conversion and >99% ee in 30 min. The rate of reaction was enhanced 1.5-fold in the presence of glucose as co-substrate

as compared to the control (no glucose). From these it can be concluded that glucose is an efficient co-substrate to generate co-factors for