Aldehydes fractionation

To identify the specific aldehyde that is actually involved in the light-emitting reaction of living luminous bacteria, Shimomura et al. (1974a) extracted and purified the aldehyde from 40 g each of the bacterial cells of P. phosphoreum, Achromobacter (Vibrio or Photobacterium) fischeri, and an aldehydeless mutant of A. fischeri. The aldehyde fractions were purified, and then oxidized with Tollens reagent (silver oxide dissolved in ammonia) to convert the CHO group into the COOH group. Then the acids obtained were analyzed by mass spectrometry. The results indicated that P. phosphoreum had contained a mixture of aldehydes dodecanal (5%), tetradecanal (63%) and hexadecanal (30%), as shown in Table 2.2. Thus, tetradecanal was clearly predominant in... 

In an electrical discharge. labelled CO2 and methane produce aldehydes (CH2 0 - 24% activity in the aldehyde fraction) and Cj- acids (40% activity in the carboxylic acid fraction) [20]. 

PbTx-1, R=CH2(=CH2)CH0 aldehyde fraction Toe PbTx-7, R=CH2(=CH2)CH20H, single reduction PbTx-10, R=CH2CH(CH3)CH20H, double reduction... 

Fig. 5.29. Total ion chromatogram of ketone+aldehyde fractions in sinking particulate material from the Yongshu Reef Lagoon. A, Cis isoprenoid ketone B, Z pritenal C, E pristenal D, Z phytenal E, E phytenal (Duan et al., 1997) (With permission from Duan Y)...

Bound SO2 also exerts a growth inhibitor effect, demonstrated by Fomachon (1963) (Section 8.6.3). Lactic acid bacteria may be capable of metabolizing the aldehyde fraction of the combination and liberating SO2. The SO2 then exerts its activity on the cell, but it is less effective. From their tests, Lafon-Lafourcade and Peynaud (1974) concluded that bound SO2 is 5 to 10 times less active than free SO2. Other authors have observed that its concentration in wine can easily be 5 to 10 times more elevated. 

By the controlled oxidation of primary alcohols with a solution of potassium or sodium dichromate in dilute sulphuric acid. To avoid the further oxidation to the corresponding acid, the aldehyde is removed as rapidly as possible by distillation through a fractionating column, for example ... 

To obtain pure acetaldehyde, the product must be redistilled. Clean and dry the 200-250 ml. flask first used, immerse it in cold or ice water pour in the crude acetaldehyde rapidly, attach the fractionating column, etc. Immerse the receiver in crushed ice. Heat the flask gently in a water bath and adjust the temperature so that the aldehyde distils slowly and at a uniform temperature. The temperature recorded at the top of the column may depend partly upon the temperature of the laboratory, if this is above 21°. Pure acetaldehyde boils at 21°. 

The experimental procedure to be followed depends upon the products of hydrolysis. If the alcohol and aldehyde are both soluble in water, the reaction product is divided into two parts. One portion is used for the characterisation of the aldehyde by the preparation of a suitable derivative e.g., the 2 4-dinitrophenylhydrazone, semicarbazone or di-medone compound—see Sections 111,70 and 111,74). The other portion is employed for the preparation of a 3 5-dinitrobenzoate, etc. (see Section 111,27) it is advisable first to concentrate the alcohol by dis tillation or to attempt to salt out the alcohol by the addition of solid potassium carbonate. If one of the hydrolysis products is insoluble in the reaction mixture, it is separated and characterised. If both the aldehyde and the alcohol are insoluble, they are removed from the aqueous layer separation is generally most simply effected with sodium bisulphite solution (compare Section Ill,74),but fractional distillation may sometimes be employed. 

Many esters occur naturally Those of low molecular weight are fairly volatile and many have pleasing odors Esters often form a significant fraction of the fragrant oil of fruits and flowers The aroma of oranges for example contains 30 different esters along with 10 carboxylic acids 34 alcohols 34 aldehydes and ketones and 36 hydrocarbons... 

The mixture is cooled and noncondensable gases are scmbbed with water. Some of the resultant gas stream, mainly hydrogen, may be recycled to control catalyst fouhng. The Hquids are fractionally distilled, taking acetone overhead and a mixture of isopropyl alcohol and water as bottoms. A caustic treatment maybe used to remove minor aldehyde contaminants prior to this distillation (29). In another fractionating column, the aqueous isopropyl alcohol is concentrated to about 88% for recycle to the reactor. 

At high enough concentrations, PAN is a potent eye irritant and phytotoxin. On a smoggy day in the Los Angeles area, PAN concentrations are typically 5 to 10 ppb in the rest of the United States PAN concentrations are generally a fraction of a ppb. An important formation route for formaldehyde [50-00-0] HCHO, is reaction 9. However, o2onolysis of olefinic compounds and some other reactions of VOCs can produce HCHO and other aldehydes. 

Another process employed to increase the formation of volatile compounds in fmit is that of bioregulators. When a bioregulator is appHed to lemon trees an increase in both the aldehyde and alcohol fractions of the lemon oil extracted from the fmit of the treated lemon trees was observed (78). 

Feints. Feints are the third fraction of the distiUation cycle derived from the distiUation of low wines in a pot stiU. This scotch term is also used to describe the undesirable constituents of the wash that are removed during the distiUation of grain whiskey in a continuous patent stiU (Coffey). These are mostiy aldehydes and fusel oils. 

Common impurities found in aldehydes are the corresponding alcohols, aldols and water from selfcondensation, and the corresponding acids formed by autoxidation. Acids can be removed by shaking with aqueous 10% sodium bicarbonate solution. The organic liquid is then washed with water. It is dried with anhydrous sodium sulfate or magnesium sulfate and then fractionally distilled. Water soluble aldehydes must be dissolved in a suitable solvent such as diethyl ether before being washed in this way. Further purification can be effected via the bisulfite derivative (see pp. 57 and 59) or the Schiff base formed with aniline or benzidine. Solid aldehydes can be dissolved in diethyl ether and purified as above. Alternatively, they can be steam distilled, then sublimed and crystallised from toluene or petroleum ether. 

The purification of diethyl ether (see Chapter 4) is typical of liquid ethers. The most common contaminants are the alcohols or hydroxy compounds from which the ethers are prepared, their oxidation products (e.g. aldehydes), peroxides and water. Peroxides, aldehydes and alcohols can be removed by shaking with alkaline potassium permanganate solution for several hours, followed by washing with water, concentrated sulfuric acid [CARE], then water. After drying with calcium chloride, the ether is distilled. It is then dried with sodium or with lithium aluminium hydride, redistilled and given a final fractional distillation. The drying process should be repeated if necessary. 

Acetal (acetaldehyde diethylacetal) [ 105-57-7] M 118.2, b 103.7-104 , d 0.831, n 1.38054, 1.3682. Dried over Na to remove alcohols and water, and to polymerise aldehydes, then fractionally distd. Or, treat with alkaline H2O2 soln at 40-45° to remove aldehydes, then the soln is saturated with NaCl, separated, dried with K2CO3 and distd from Na [Vogel J Chem Soc 616 1948]. 

Cyclohexanol [108-93-0] M 100.2, m 25.2", b 161.1", d 0.946, n 1.466, n s 1.437, n 1.462. Refluxed with freshly ignited CaO, or dried with Na2C03, then fractionally distd. Redistd from Na. Further purified by fractional crystn from the melt in dry air. Peroxides and aldehydes can be removed by prior washing with ferrous sulfate and water, followed by distillation under nitrogen from 2,4-dinitrophenylhydrazine, using a short fractionating column water distils as the azeotrope. Dry cyclohexanol is very hygroscopic. 

The acetal (b 82.5°) is removed during fractional distn. Traces of benzene, if present, can be removed as the benzene/MeOH azeotrope by distn in the presence of MeOH. Distn from LiAlHa removes aldehydes, peroxides and water. Dioxane can be dried using Linde type 4X molecular sieves. Other purification procedures include distn from excess C2H5MgBr, refluxing with Pb02 to remove peroxides, fractional crystn by partial freezing and the addition of KI to dioxane acidified with aq HCl. Dioxane should be stored out of contact with air, preferably under N2. 

---