Higher aldehydes

Published work on the oxidation of aldehydes higher than propion-aldehyde at intermediate and high temperatures is not yet extensive, although Baldwin et al, [109] have shown that the behaviour of z-butyr-aldehyde is similar to that of propionaldehyde. 

---

Note. The 2,4-dinitrophenylhydrazones of many higher aldehydes and ketones may be insoluble in most solvents. In this case, Mter them off, wash with ethanol, dry and take the m.p. attempted recrystallisation may cause partial decomposition. (M.ps., pp. 530-540.)... 

The use of a-bromoaldehydes, more reactive than the a-chloro derivatives, gives better results (492,512). They have permitted the yields of the cyclization to be increased from 8 to 60% in the latter case. With the higher aldehydes the yields decrease. Thus for 5-f-butylthiazole it is not higher than 7 to 20% (492, 512). On the other hand, cr-bromoaldehydes are particularly difficult to obtain. 

Although stoichiometric ethynylation of carbonyl compounds with metal acetyUdes was known as early as 1899 (9), Reppe s contribution was the development of catalytic ethynylation. Heavy metal acetyUdes, particularly cuprous acetyUde, were found to cataly2e the addition of acetylene to aldehydes. Although ethynylation of many aldehydes has been described (10), only formaldehyde has been catalyticaHy ethynylated on a commercial scale. Copper acetjlide is not effective as catalyst for ethynylation of ketones. For these, and for higher aldehydes, alkaline promoters have been used. 

Chemical safety data sheets for individual compounds should be consulted for detailed information. Precautions for the higher aldehydes are essentially those for most other reactive organic compounds, and should include adequate ventilation in areas where high exposures are expected fire and explosion precautions and proper instmction of employees in use of respiratory, eye, and skin protection. 

Reactions and Uses. The common reactions that a-hydroxy acids undergo such as self- or bimolecular esterification to oligomers or cycHc esters, hydrogenation, oxidation, etc, have been discussed in connection with lactic and hydroxyacetic acid. A reaction that is of value for the synthesis of higher aldehydes is decarbonylation under boiling sulfuric acid with loss of water. Since one carbon atom is lost in the process, the series of reactions may be used for stepwise degradation of a carbon chain. 

Other Aldehydes. The higher aldehydes react with phenol in much the same manner as formaldehyde, although at much lower rates. 

Urea—Other Aldehyde Reaction Products. Urea can also react with other aldehydes to form slow release nitrogen fertilizers. However, cost constraints associated with higher aldehydes have either precluded or limited broad commercial development of these products. Two exceptions are isobutyhdene diurea (IBDU), registered trademark of Vigoro Industries, and crotonyHdene diurea (CDU), registered trademark of Chisso-Asahi Fertilizer Co. 

Examples are given of common operations such as absorption of ammonia to make fertihzers and of carbon dioxide to make soda ash. Also of recoveiy of phosphine from offgases of phosphorous plants recoveiy of HE oxidation, halogenation, and hydrogenation of various organics hydration of olefins to alcohols oxo reaction for higher aldehydes and alcohols ozonolysis of oleic acid absorption of carbon monoxide to make sodium formate alkylation of acetic acid with isobutylene to make teti-h ty acetate, absorption of olefins to make various products HCl and HBr plus higher alcohols to make alkyl hahdes and so on. 

Schimmel Co. have prepared a number of fatty aldehydes bj a modification of this reaction. They distilled mixtures of barium formate with the barium salt of the corresponding acid, in a vacuum, as it was well known that this increases the yield when working with the higher aldehydes, which volatilise with difficulty. 

Here the rate constants k refer to the rates of the numbered reactions above the value ho2/ro2 an average for different R02 entities. The A term accounts for HOjj production via ozone photolysis R1-R3, the Bj term accounts approximately for the source from aldehyde photolysis (R12 plus higher aldehydes), and the B2 term is a composite source from formaldehyde (RIO) and dicarbonyls (Cj) less the HOjj sink from PAN formation (R22) B2=Ci-C2). Values for Bj,... 

Currently, worldwide production of aldehydes exceeds 7 million tons/year (1). Higher aldehydes are important intermediates in the synthesis of industrial solvents, biodegradable detergents, surfactants, lubricants, and other plasticizers. The process, called hydroformylation or more familiarly, the Oxo process, refers to the addition of hydrogen and the formyl group, CHO, across a double bond. Two possible isomers can be formed (linear or branched) and the linear isomer is the desired product for these applications. 

One approach that has been successfully used to separate the catalyst from the product aldehyde is to use a biphasic system in which the rhodium catalyst is soluble in water and the product is soluble in an organic phase. This approach is used by Hoechstdlhone-Poulenc to produce more than 600,000 t/year of butyraldehyde (a lower aldehyde) (2). Unfortunately, this process caimot be used to produce higher aldehydes because the water solubihty of the higher olefins that are the feedstock is very low, which dramatically reduces the reaction rate. 

Suitable for conversion of higher olefins to higher aldehydes. 

Pettit and coworkers—metal hydride intermediates by weak base attack over Fe carbonyl catalysts. Pettit et al.ls approached the use of metal carbonyl catalysts for the homogeneous water-gas shift reaction from the standpoint of hydroformyla-tion by the Reppe modification.7 In the typical hydroformylation reaction, an alkene is converted to the next higher aldehyde or alcohol through reaction of CO and H2 with the use of a cobalt or rhodium carbonyl catalyst. However, in the Reppe modification, the reduction is carried out with CO and H20 in lieu of H2 (Scheme 6) ... 

Electrochemical oxidation of higher aldehydes (56) in the presence of secondary... 

S-Protonated Aryliminium Salts Hesse has made a much more extensive study of the reaction of aryl primary amines (58) with higher aldehydes (see 59) and a suitable alkene, usually styrene or a-methylstyrene, and found that high yields of tetra-hydroisoquinoline (60) could be obtained even when an electron-withdrawing group was present in the aryl ring. Carbonium ion (61) appeared likely as an intermediate. 

Replacement of formaldehyde In amlnoplasts by substitution with higher aldehydes (or ketones) Is even more problematic the equilibrium of the condensation shifts strongly towards starting materials, except In cases where the formaldehyde replacement contains electron withdrawing substituents (e.g. with glyoxal... 

A side reaction occurring with acetaldehyde and higher aldehydes containing a-hydro-gens is aldol condensation [Hashimoto et al., 1976, 1978 Yamamoto et al., 1978], Aldol reaction can be extensive at ambient temperatures and higher but is avoided by polymerization at low temperature. 

Competing side reactions in cationic polymerization of carbonyl monomers include cyclotrimerization and acetal interchange. Cyclotrimerization is minimized by low-polarity solvents, low temperatures, and initiators of low acidity. Acetal interchange reactions among different polymer chains do not occur except at higher temperatures. Acetaldehyde and higher aldehydes are reasonably reactive in cationic polymerization compared to formaldehyde. Haloaldehydes are lower in reactivity compared to their nonhalogen counterparts. 

Figures 4.26, 4.27, and 4.28 show typical UV absorption spectra for some simple aldehydes and ketones (Rogers, 1990 Martinez et al., 1992 see also Cronin and Zhu, 1998, for n-pentanal). Formaldehyde stands out from the higher aldehydes and ketones in that it has a highly structured spectrum and furthermore, the absorption extends out to longer wavelengths. The latter difference is particularly important because the solar intensity increases rapidly with wavelength here (Chapter 3.C.1) and hence the photolysis rate constant for HCHO and the rate of production of free radicals...

The photolysis of higher aldehydes, RCHO, also forms HCO (see Chapter 4) and hence H02 ... 

However, as discussed in Chapter 4, the absorption spectrum of higher aldehydes cuts off at shorter wavelengths than formaldehyde. This, combined with higher quantum yields for radical production in the 290- to 340-nm range and the fact that HCHO produces 2H02 essentially immediately upon dissociation, makes the photolysis of aldehydes larger than formaldehyde less important at equal concentrations of the aldehydes. 

Puxbaum, H., Biogenic Emissions of Alcohols, Ester, Ether, and Higher Aldehydes, in Biogenic Volatile Organic Compounds in the Atmosphere (G. Helas, J. Slanina, and R. Steinbrecher, Eds.), pp. 79-99, SPB Academic Publishing, Amsterdam, 1997. 

Figure 15.12 summarizes the ratio of indoor-to-outdoor concentrations of HCHO and higher aldehydes as well as formic and acetic acids measured in some conventional homes. Concentrations of all of these compounds, except possibly propionaldehyde, are significantly higher indoors, suggesting that not only... 

Acetaldehyde and higher aldehydes ALD Peroxy radicals with carbonyl groups ... 

FIGURE 16.18 Concentration-time profiles for 03, NO., NMHC, H202, HCHO, and higher aldehydes (RCHO) predicted using four different chemical submodels two carbon bond four models (CB4.1 and CB4-TNO), a RADM model (RADM2), and the EMEP model (adapted from Kuhn et al., 1998). 

---