Green aspect

In contrast, the energy gain of ethanol fermentation from a cellulose-based crop was estimated at only 10% [31]. A fife cycle assessment of bioethanol from wood came to a similar conclusion [32]. This unsatisfactory outcome mainly results from the energy-intensive pretreatment with steam explosion, such as is used by Iogen [16]. The replacement of the latter by COz explosion [33] may redress the energetic balance. 

The unfavorable energy balance notwithstanding, the fermentation of ethanol, as well as other chemicals, from lignocellulose hydrolysate is considered highly desirable by some to avoid competition with food production. We note, however, that the large scale processing of waste lignocellulose runs counter to sensible 

The industrial production of lactic acid [34, 35], which dates back to 1881, is undergoing a remarkable transition. Lactic acid used to be a fairly mature fine chemical that was produced, in the mid 1990s, at a volume of 50-70 kt a1 worldwide. A major share (25 kt a-1, including simple esters etc.) is used in the food industry. 

This is now changing, as a new and very big player has entered the field. Cargill (USA), which in the late 1990s started to push fermentatively produced lactic acid as an emerging commodity [39], has opened a production facility with a capacity of 140 kt a-1 of polylactic acid in 2002 [40] a market potential of 500 kt a-1 of lactic acid products in 2010 is anticipated. 

Lactic acid is produced chemically from acetaldehyde, by hydrocyanation, followed by acid hydrolysis of the cyanohydrin (Fig. 8.6 a). The cmde lactic acid is purified via esterification with methanol, distillation of the ester and hydrolysis with recycling of the methanol [34]. Major drawbacks are the production of an equivalent of ammonium sulfate and the cumbersome purification procedure that is required to obtain food-grade lactic acid. 

---

The choice of reaction solvent is also of concern in the synthesis of new TSILs. Toluene and acetonitrile are the most widely used solvents, the choice in any given synthesis being dictated by the relative solubilities of the starting materials and products. The use of volatile organic solvents in the synthesis of ionic liquids is decidedly the least green aspect of their chemistry. Notably, recent developments in the area of the solventless synthesis of ionic liquids promise to improve this situation [10]. 

The synthehc applicability of arsenates is restricted by their toxicity that avoids the green aspect of the enzymatic processes. Wong et al. have shown that the use of inorganic borate buffer allows L-rhamnulose-l-phosphate aldolase (Rha-IPA) to accept DHA as substrate, although the of the reaction is about 50 times lower than with the natural substrate [10]. In spite of this fact, these authors have successfully used this approach for the one-step synthesis of L-fructose and L-rhamnulose, and for the facile two-step synthesis of several L-iminocyclitols. 

Likewise Bi(OTf)3 catalyzes the reaction of aziridines to give the corresponding (3-amino alcohols (Fig. 8). In the case of cycloalkyl aziridines, the stereochemistry of the ring-opened products was found to be trans. This method has some additional features of green aspects as it allows the recovery and re-usability of the catalyst. 

Curylo, J., W. Wardencki, and J. Namiesnik. 2007. Green aspects of sample preparation—a need for solvent reduction. Pol. J. Environ. Stud. 16 5-16. 

The interest in FDA arises from its possible application as a renewable-derived replacement for terephthalic acid in the manufacture of polyesters. A multitude of oxidation techniques has been applied to the conversion of HMF into FDA but, on account of the green aspect, platinum-catalyzed aerobic oxidation (see Fig. 8.35), which is fast and quantitative [191], is to be preferred over all other options. The deactivation of the platinum catalyst by oxygen, which is a major obstacle in large-scale applications, has been remedied by using a mixed catalyst, such as platinum-lead [192]. Integration of the latter reaction with fructose dehydration would seem attractive in view of the very limited stability of HMF, but has not yet resulted in an improved overall yield [193]. 

CIC The basic acid taste results from high levels of oxalic and succinic acid. (Z)-3-hexenol and (E)-2-hexenal contribute to the unripe, green aspect and ethyl benzoate with methyl-2-hydroxybenzoate are the typical medicinal notes. Quinoline and ethyl nicotinate add the earthy background. 

We have already made reference to green aspects of organometallic chemistry in Section 7-2-1, where environmentally-friendly characteristics of the activation of H-H, C-H, and C-C bonds were pointed out. In this section, we focus on the relationship between green chemistry and organometallic chemistry. Green chemistry is defined as the utilization of a set of principles that reduces or eliminates... 

More recently, a protocol was elucidated by Malezcka and Smith to produce aryl borate esters directly without first producing aryl halides.144 The reaction involves an Ir-catalyzed C-H activation (Section 7-2-1) to yield the aryl borate, which can then be used directly in Suzuki cross-coupling (equation 12.71). This new development adds another green aspect to Suzuki cross-coupling, which is already a relatively green synthesis tool. 

Certainly, for most synthetic chemists the concern about the green aspects is nowadays present in their search for new synthetic methods. Green aspects are then put in evidence in the corresponding publications. Most often, however, this is apphed to any method discovered that allows making a compound to react in a way that is either impossible by conventional chemistiy, or possible only under severe conditions. This is something that is new and can be added to the choice of methods a synthetic chemist has available. Typically, a catalyst is used that makes the reaction occur under milder conditions. 

This chapter is subdivided in two parts, the first briefly introduces the green aspect of photochemistry in synthesis, while the second outlines a series of representative reactions, subdivided according to the process involved. 

Green Aspects of Direct Arylation of Aryl C-H Bonds... 

In future, by using wood, or one of its components, as a renewable resource, the entire process chain or an entire reaction system can be regarded under green aspects including energy efficiency. 

We assume that the safe computer consists of two identical sub-systems, i.e. the channels. Both channels are crosschecked, so that the safe computer would allow a less restrictive state only, if both channels give the same result. If the results from both channels differ, the less restrictive state would not be allowed, but a failure message would be issued. A less restrictive state could e.g. be a railway sign showing a green aspect. 

I don t really know since we only did one lab in green chemistry and the green aspect was really underplayed. 

FIGURE 6.14 Radial pentagon for synthesis of 2-phenylpropionitrile [12]. The green aspect of this reaction is that dimethylcarbonate was used as a benign methylating agent. 

---