NotesChem2364Sum09

NotesChem2364Sum09 - Experiment 1a: Decolorization...

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Experiment 1a: Decolorization Decolorization: This technique uses activated charcoal (also known as decolorizing carbon) to remove color impurities from starting materials or products. The activated carbon consists of very fine particles with a very large surface area for absorbing large polar molecules (such as colored compounds). You must be careful to avoid using too large of an amount of carbon because then you risk absorbing your product. To water suction device Use thick wall tubing (Red) 1
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Experiment 1b: Acid – Base Extraction Acid – Base Extraction: It is a liquid-liquid extraction that is based on the acid/base properties of compounds. The extraction is performed by using two immiscible solvents, one is aqueous and the other one organic. If a compound is soluble in water then Acid-Base extraction is not the appropriate method of separation. On the other hand, if a compound is insoluble in water and it has acid/base properties then it can be extracted by using Acid-Base Extraction. Solubility in Water Rules Ionic Compounds: Sufonates, Carboxylates, and Aminium Salts. H-Bonding Compounds: Alcohols, Carboxylic Acids (4C or less) Phenol is soluble, others are insoluble Amides (5C or less) Primary Amines (4C or less) Secondary Amines (6C or less) Dipole-Dipole Compounds: Tertiary Amines: (6C or less) Aldehydes, Ketones (4C or less) Esters, Nitriles (3C or less) Dimethyl ether, nitromethane, Chloromethane are soluble. Non-Polar compounds are insoluble in water: hexane, benzene, carbon tetrachloride. 2
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Alkyl halides, Nitrocompounds, and Ethers are insoluble with the exceptions already mentioned before. Determine whether the following compounds are soluble or insoluble in water: ethanoic acid (acetic acid) 1,4-dichlorobenzene 4-ethylaniline 3,5-dimethylphenol The organic solvent (layer, or phase) must be water insoluble, have a low boiling point, and be relatively non-toxic, for instance: CH 2 Cl 2 , Dichloromethane (DCM) CH 3 CO 2 CH 2 CH 3 , Ethyl Acetate (EtOAc) The aqueous solvent (layer, or phase) could be: Aqueous acid – HCl(aq) in case the compound to extract is basic, for instance amines. Aqueous base – NaHCO 3 (aq) in case that the compound to extract has a pKa lower than 6, for instance carboxylic acids (4-5 pKa). NaOH(aq) in case that the compound to extract has a pKa lower than 15, for instance 3
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carboxylic acids (4-5 pKa), phenols (9-10 pKa) pKa Table pKa acid base 16-18 ROH RO - 15.7 H 2 O HO - 10-11 R 3 NH + R 3 N 9.5-10 ArOH ArO - 6.4 H 2 CO 3 HCO 3 - 4.8-5 RCO 2 H RCO 2 - 4.6 ArNH 3 + ArNH 2 -1.74 H 3 O + H 2 O As Acidity increases Basicity decreases : Acidity of compounds that consist of any element bonded to H increases from left to right and from top to bottom in the periodic table. for acidity: HBr > HCl > HF > H
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NotesChem2364Sum09 - Experiment 1a: Decolorization...

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