Hardness reactions

From reactions 2—6, it can be seen that the addition of lime always serves three purposes and may serve a fourth. It removes, in order, COg, calcium carbonate hardness, and magnesium carbonate hardness (reactions 8, 9, and 10, respectively). Where magnesium noncarbonate hardness must be removed, the lime converts it to calcium noncarbonate hardness (reaction 6). Soda ash, then, removes noncarbonate hardness according to reaction 5. 

Starting from molecular pre-catalysts some signs can pointed to the formation of metallic NPs colour changes during the reaction or precipitate formation are observed, or induction time is determined, or hard reaction conditions (high temperature and/or high pressure) are used, or potential stabilisers for metal nanoclusters are present... 

The combination of the dual electrophilic character of DMC with its reaction products allows two consecutive steps to occur in a selective way for what concerns both reaction sequence and yields first, the hard-hard reaction occurs and produces a soft anion only and second, a soft-soft nucleophilic displacement leads to the final product. Since hard-soft and soft-hard interactions are inhibited, double methylation and double carboxymethylation do not occur. 

Foodstuff Mai Hard Reaction Oxidation Enzymatic Degradation other Reactions... 

Choi, S.J., Kim, H.J., Park, K.H., Moon, T.W. (2005). Molecular characteristics of oval-bumin-dextran conjugates formed through the Mai Hard reaction. Food Chemistry, 92, 93-99. 

The role of the catalyst is very important in the latter step, which requires hard reaction conditions (M. Aresta et al. unpublished results). In particular, by using metal oxides characterized by a specific ratio between the acid and basic sites [242] as catalyst, conversion of the carbamate into the carbonate is very much improved, together with selectivity (the conversion into carbonate increases as the acid/basic site ratio decreases). 

In addition to the products generated by the Mai Hard Reaction other routes exist for the formation of aromas via thermal processes. 

The most important steps of thermal aroma formation via the Mai Hard reaction are ... 

Sugars as well as amino acids are decomposed by heat treatment. The final reaction products from sugars are often identical with the products formed by the Mai Hard reaction. 

Figure 9 Difference in the nature of the reaction cavity in soft and hard reaction media. Top Hard reaction cavity, cavity free volume fixed. Bottom Soft reaction cavity, flexible cavity free volume.

Supercritical Water Oxidation (SCWO) has been proved to be a suitable process for treatment of several toxic and hazardous organic wastes due to its high removal efficiency. SCWO requires of hard reaction conditions (22.1 MPa and over 374°C). Special reactors are needed to support these conditions. An original reactor design is presented here wich has been tested in the treatment of alcohols+ammonia solutions in water. Performance results are presented here for ammonia and alcohols. Destruction efficiency greater than 99.9% are reached for both compounds, probing the correct performance of the reactor. 

The Mai Hard reaction involves attack of the nitrogen of the amino group on the carbon atom of the carbonyl, sometimes followed by removal of water to produce the Schiff base (17.) (Figure 7). Detailed coverage of the Maillard reaction is given elsewhere in this volume by Hodges (18), so only a few examples, particularly those with which the author has had some relation-... 

There are, of course, many carbonyl compounds formed by hydrolytic or oxidative deteriorations of lipid constituents, and most of these are potentially capable of entering into Mai Hard reactions with proteins. One such product is reputedly malon-aldehyde (26) (Figure 10). 

LiF( ) is a very favorable hard-hard reaction LiF is only slightly soluble. AgF( ) is a soft-hard reaction that is not favored AgF is moderately soluble. 

A hard-hard reaction is fast because of a large Coulombic attraction. 

We can assert that anions 1 and 2 give different compounds since they have different soft/hard character. Their difference in hardness provides a reason for the discrimination observed between the two electrophilic centers of DMC. The hard nucleophile 1 attacks only the carbonyl of DMC (eq. 5), while the anion of the product 2 is a softer nucleophile thus it selectively produces the methyl derivative (eq. 6). The change in hardness/softness of the anion, due to the presence of the carboxymethyl group, is enough to significantly alter the reactivity of the DMC molecule. The combination of the dual electrophilic character of DMC with its reaction products allows two consecutive steps to occur in a selective way both in the reaction sequence and yield first the hard-hard reaction occurs and produces only a soft anion then a soft-soft nucleophilic displacement leads to the final product. Since hard-soft and soft-hard interactions are inhibited, neither double methylation nor double carboxymethylation take place. 

Both of these centres were selectively carboxymetliylated (hard reaction, Scheme 13). Classical metal catalysts such as Pb(0Ac)2 or Sn[O2CCH(Et)Bu]2 effected N-2 activation under refluxing conditions (Table 10, entries 4-6) whilst potassium /-butoxide at room temperature activated N-1 (Table 10, entiy 1). It was reasoned that the reaction with a strong base was due to the deprotonation of N-1 creating an anion with hard nucleophilicity... 

Slippage experiments involved extremely hard reaction conditions the macrocycle was melted at 350°C in the presence of the dumbbell component during very short periods of time (10 min). A [2]-rotaxane was obtained in 3% yield by this method and was shown to be stable at room temperature in dmf solution [106]. 

Nucleophilic addition using organometallics showed that the C-4 position of (la) is a hard reaction site, whereas the C-5 position has soft reactivity (Equation (15)) <85CC1370>. These results are in accord with those from MO calculations. Softer nucleophiles such as organocopper reagents underwent a redox reaction with triazine to give 2,5-dihydro derivatives without ring substitution. 

The concepts of PMO and frontier orbital theory can be related to the characteristics of hard-hard and soft-soft reactions. Recall that hard-hard reactions are governed by electrostatic attractions, whereas soft-soft reactions are characterized by partial bond formation. The hard-hard case in general applies to situations in which there is a large separation between the HOMO and LUMO orbitals. Under these conditions the stabilization of the orbitals is small and the electrostatic terms are dominant. In soft-soft reactions, the HOMO and LUMO are close together, and the perturbational stabilization is large. 

Among the Ni/Mg/Al samples, the microwave-treated SAl catalyst is more active and selective towards syngas than the merely stirred catalyst BOl. However, under hard reaction conditions differences are less important. In fact, with very active and selective catalysts, differences can be smoothed by a temperature increase, which displaces the reaction towards the equilibrium. When using diluted mixtures the heat produced in the exothermic reaction is reduced, thus achieving a better control of the temperature inside the catalytic bed. For this reason the beneficial effect of the MWHT aging treatment was more notable in the tests carried out at 500°C. 

These tests indicate that the catalytic performance of the prepared salts remains relatively good even in conditions at which the structure partly decomposes this makes particularly promising the utilization of these salts as catalysts also in the presence of particularly hard reaction conditions. 

The especially widespread occurrence of the less oxidized corresponding di-and tetrahydroisoquinolines in both families (see Sections II and III) requires more detailed considerations on the biological source of the nitrogen, also in view of the uncommon use of the toxin ammonia outside the primary metabolism (57). Moreover, formation of fully conjugated isoquinolines according to Scheme 3 would necessitate a subsequent hydrogenation of the resulting stable aromates 33 and 35, a biochemically unusual reaction type (5), which also, chemically, requires relatively hard reaction conditions (e.g., Zn-HCl, see Section V,C,3). 

An acceptable definition of local hardness and subsequent identification of the hard sites in a molecule is, therefore, in demand [298-304], The minimum Fukui function rule [301] asserts that hard reactions, unlike softer ones, would prefer sites with minimum Fukui function values. Although there are applications [305-307] of this rule, subsequent criticisms [303, 308] are also reported. The minimum Fukui function rule is unable to correlate the electrostatic hard-hard interactions that are predominantly charge-controlled with hardly any relevant effect from the associated frontier orbitals. The given rule cannot justify the inadequacy of the frontier orbitals and also misses the role of electrostatic interactions in hard-hard interactions [303, 304, 308]. 

In chocolate manufacturing, NaHCOs enhances the Mai Hard reaction, providing dark bitter chocolates. 

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