Find the Concentration of Malon Acid in Each Solution

Additions to CX π-Bonds, Part 2

Lutz F. Tietze , Uwe Beifuss , in Comprehensive Organic Synthesis, 1991

1.11.3.1.3 Malonic acid

Malonic acid undergoes Knoevenagel condensations with nearly every type of aldehyde and with very reactive ketones. ³ If condensations with malonic acid are performed in ethanolic ammonia below 70   °C, the methylenemalonic acids are usually obtained. If, however, the condensations are performed in pyridine (Doebner modification), decarboxylation normally takes place and the acrylic or cinnamic acid is formed (see also Section 1.11.2.3). In these reactions the double bond isomer with the carboxyl group trans to the larger substituent is usually obtained (see also Section 1.11.2.5). ^3,135,136 A problem with condensations of malonic acid is the isomerization of the α,β-isomer to the 3,-y-isomer. ^3,84 Coumarin-3-carboxylic acid ( 87 ) and related compounds are obtained in the reaction of salicylaldehyde and other 3-hydroxy aldehydes with malonic acid. ^3,26,117 Finally, reaction of o-aminobenzaldehyde with malonic acid yields 2(1H)-quinolone ( 88 ). ³ The condensation of aldehydes with 2-alkylmalonic acids is of limited synthetic value as the reaction is susceptible to steric hindrance. ³ In these cases the β-hydroxy acids instead of a-alkyl-α β,-unsaturated acids can be obtained, depending on the reaction conditions. ^58,60,137 An example from the porphyrin field illustrates the problem of prediction in chemical reactivity. Condensation of 5-formyloctaethylporphyrin with malonic acid delivers compound ( 89 ) which is double decarboxylated under conditions of catalytic hydrogenation to give ( 90 ). The desired compound ( 92 ), however, is obtained by hydrogenation of half-ester ( 91 ). ¹¹⁴ Monoalkyl malonates, obtained by partial hydrolysis of dialkyl malonates, show a reactivity similar to malonic acid. The Knoevenagel reaction is usually accompanied by decarboxylation, giving a cinnamic ester. ^138,139 Addition of halogen to the double bond with subsequent dehydrohalogenation is a method for the preparation of alkynic acid esters. ¹⁴⁰

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Pyrolysis of Various Derivatives of Carboxylic Acids

Serban C. Moldoveanu , in Pyrolysis of Organic Molecules (Second Edition), 2019

Anhydrides of Dicarboxylic Acids

Malonic acid anhydride is not a very stable compound. Diethylmalonic acid anhydride is relatively stable and at 160–180°C, decomposes to form diethylketene and CO ₂, as shown in the following reaction:

(14.4.2)

A similar reaction is given by dimethylmalonic anhydride, but the reaction products tend to form a dimer or a polymer.

Succinic acid anhydride and glutaric acid anhydride are relatively stable molecules. Their decomposition at temperatures above 300°C and a heating time as long as 6   h generates CO₂ and condensation products. Adipic anhydride by pyrolysis around 240°C generates CO₂ and cyclopentanone, as shown in the following reaction:

(14.4.3)

Similarly, dimethyl- and trimethylpimelic anhydrides generated dimethyl and trimethyl cyclohexanones, respectively [5].

Maleic acid anhydride is also a relatively stable compound, and its decomposition rate as a function of temperature is given by an Arrhenius equation of the form:

(14.4.4) $k={10}^{+14.33\pm 0.3}+exp\left[-\left(60.9\pm 1\text{kcal}\right)/\mathit{RT}\right]$

For 1   s exposure time, the rate of decomposition is displayed in Fig. 14.4.1 [6].

Fig. 14.4.1. Decomposition of maleic anhydride as a function of temperature.

The decomposition reaction is shown below:

(14.4.5)

The reaction appears to proceed by a concerted mechanism. The reaction was studied at pressures from about 0.7 to 20   Torr. No propionaldehyde or propionic acid was detected in the pyrolyzate. A condensation product is generated from phthalic anhydride when heated for 1   h at 250°C [5].

More complex anhydrides also were studied regarding their thermal decomposition products. One example is the anhydride of dihydroabietic acid. Pyrolysis of this compound generates CO and various decomposition products involving, besides the anhydride functionality, the rest of the dehydroabietic acid [7].

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Synthesis: Carbon With No Attached Heteroatoms

J. Blanchet , ... Jieping Zhu , in Comprehensive Organic Functional Group Transformations II, 2005

1.02.3.4.1 Thermal decarboxylation of disubstituted malonic acids

Refluxing disubstituted malonic acids in aprotic solvent is a convenient procedure to achieve decarboxylation. Simple reflux in dioxane <1999SL1371> or toluene <2001TL6015> generally provides high yields of the corresponding carboxylic acid. Microwave heating was found to effect rapid decarboxylation of malonic acids in water (190   °C, 800 W, 15 min, 80–98%) <2000SC2099>.

Similarly, heating malonic acid derivatives in acetic acid <1995SC521, 2000JMC4868> led to high yields of the corresponding acids. These conditions have found broad utility in organic synthesis. It is worth noting that unusual stereoselective decarboxylation has been reported as a key reaction in an industrial synthesis of carbapenem antibiotic (Equation (125)) <1995JOC8367>.

(125)

From extensive computational studies, the authors concluded that the selectivity observed was derived from a kinetically controlled protonation of the intermediate ketene acetal.

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Enzymatic Plastic Degradation

Lili Tian , ... Rong Ji , in Methods in Enzymology, 2021

2.1.1 Materials

•

Malonic acid (solid, chemical purity 98%)

•

Cinnamic acid (solid, chemical purity 98%)

•

Piperidine (10.9   mol   L^{−   1}, chemical purity 99.5%)

•

Benzaldehyde (9.8   mol   L^{−   1}, chemical purity 99.5%)

•

Pyridine (12.4   mol   L^{−   1}, chemical purity 99.5%)

•

Ethyl acetate (10   mol   L^{−   1}, chemical purity 99%)

•

n-Hexane (7.7   mol   L^{−   1}, chemical purity 99%)

•

Formic acid (26.5   mol   L^{−   1}, chemical purity 99.5%)

•

Sodium sulfate (anhydrous Na₂SO₄, solid, chemical purity 99%)

•

Silver acetate (AgOAc, solid, chemical purity 99%)

•

Potassium carbonate (K₂CO_3, solid, chemical purity 98%)

•

N,N-dimethylacetamide (DMAc, 10.8   mol   L^{−   1}, super dry solvent, chemical purity 99.5%)

•

Developer (10   mL n-hexane, ethyl acetate 10   mL and formic acid 0.1   mL)

•

Hydrochloric acid (HCl, chemical purity 99%, 1   mol   L^{−   1}, 43   mL 12   M concentrated HCl dissolved in 457   mL water)

•

Sodium bicarbonate (NaHCO₃, chemical purity 99%, 0.6   mol   L^{−   1}, 5   g NaHCO₃ dissolved in 100   mL water)

•

Sodium chloride (NaCl, chemical purity 99%, 6   mol   L^{−   1}, 36   g NaCl dissolved in 100   mL water)

•

Sodium hydroxide (NaOH, chemical purity 99%, 1   mol   L^{−   1}, 4   g NaOH dissolved in 100   mL water)

•

[β-¹⁴C]-malonic acid (2100   MBq   mmol^{−   1}, Moravek Biochemicals, USA)

•

[U-ring-¹⁴C]-cinnamic acid (130   MBq   mmol^{−   1}, Moravek Biochemicals, USA)

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Formation and Reactivity of 5-Aminopenta-2,4-Dienals

Bernard Delpech , in Advances in Heterocyclic Chemistry, 2014

5.1.3 Active Methylene Compounds

Reaction of malonic acid and of its diethyl ester with Zincke aldehydes has been shown to afford double addition products, with elimination of the dialkylamino moiety ( 61CB234). Condensation of N,N-dimethylaminopenta-2,4-dienal with Meldrum's acid, in the presence of pyridine, gave the pentamethine derivative (91JCS(P2)2003) (Scheme 29).

Scheme 29.

A route toward near-infrared fluorescent voltage-sensitive dyes was developed recently, using TiCl₄ and Hünig's base for the alkylidenation step (09OL4822) (Scheme 30).

Scheme 30.

A Wadsworth–Emmons reaction was achieved with triethyl phosphonoacetate (67BAU1282) and this type of olefination was a method for the synthesis of isotopically labeled phenylalanine (99EJO2609) (Scheme 31).

Scheme 31.

The cyclopentadienyl anion could be condensed with a Zincke aldehyde giving a fulvene derivative which, by heating, led to azulene (57LA79) (Scheme 32).

Scheme 32.

Scheme 33.

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Quinolones as prospective drugs: Their syntheses and biological applications

Ashraf A. Aly , ... Stefan Bräse , in Advances in Heterocyclic Chemistry, 2021

2.1.2 Using phenyl malonamides

Intramolecular cyclization of malonic acid monophenyl amide 9 to form 4-hydroxy-2(1H)-quinolone is a convenient procedure. Either Eaton's reagent (phosphorus pentoxide in methanesulfonic acid) ⁴¹ or PPA ^{42 , 43} was chosen as cyclization reagents to avoid decarboxylation of the starting amide (Scheme 7).

Scheme 7.

Similarly, synthesis of 4-hydroxy-2(1H)-quinolones I was also observed via direct cyclization of N,N-diphenyl malonamides 10 in the presence of PPA at 140–150°C. ^{30 , 44} (Scheme 8).

Scheme 8.

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Step Polymerization

Francesco Pilati , in Comprehensive Polymer Science and Supplements, 1989

17.3.1 Polyesters from Aliphatic Diols and Diacids

Except for oxalic and malonic acids, which decarboxylate to an appreciable extent even at temperatures as low as 170  °C, ^306,307 aliphatic dicarboxylic acids are suitable starting monomers for direct esterification with aliphatic diols. Because of their low melting temperature, polyesters from aliphatic diols and dicarboxylic acids are most conveniently prepared by direct esterification in the melt at high temperature (180–230   °C). In order to avoid decarboxylation, polyoxalates and polymalonates are more conveniently prepared from the corresponding diesters rather than from the diacids. Alcoholysis of diesters in the presence of suitable catalysts can also be used to prepare aliphatic polyesters from dicarboxylic acids with a higher number of carbon atoms, but the higher cost of diesters makes this method of synthesis less suitable unless extremely low values of carboxyl end-groups in the resulting polyester are desired.

Anhydrides can replace the parent acids in the reaction with glycol; both succinic and maleic anhydrides are readily available and are used alone or in combination with other comonomers to prepare saturated and unsaturated polyesters, respectively.

Aliphatic polyesters can also be prepared from diols and diacyl chlorides in solution, preferably at high temperature, whilst the interfacial procedure is not used because glycols do not usually give an effective concentration of alkoxide ions in the presence of water. ³⁰⁸

This class of polyesters is characterized by low melting points and low hydrolytic stability and, consequently, these polymers have only limited industrial applications, mainly as copolymers.

Many aliphatic polyesters have been prepared from C₂–C₁₉ aliphatic dicarboxylic acids and various diols, and have been characterized for thermal transitions ^306,307 and crystalline structure. ^309–311

The chemical structure of both diol and diacid moieties obviously influences the properties of the resulting polyesters, and odd–even effects lead to a zigzag alternation of melting points on changing the length of diol and diacid.

More rigid glycols, such as 1,4-cyclohexanedimethanol, may be used to increase the melting point of polyesters. Neopentyl glycol, which does not have hydrogen atoms in the β position with respect to the ester groups, leads to polyesters with higher thermal and hydrolytic stabilities ²⁹² and many formulations use it to replace all or part of other glycols. For example, hydroxy-terminated polyesters of adipic acid with neopentyl glycol are suitable for preparing polyurethane foams which are tough, have good resistance to discoloration and possess superior hydrolytic and thermal stabilities. ³¹² Highly hindered diols such as 2,2,4,4-tetramethyl-1,3-cyclobutanediol or 2,2,4-trimethyl-1,3-pentanediol were found to be exceptionally stable to hydrolysis. ³¹³

By contrast, polyesters from oxalic and malonic acid are more susceptible to hydrolytic and thermal degradation and have therefore found few applications in the polymer field; however, the dimethyl-substituted malonic acid leads to polymers of higher melting points and stabilities. ³¹⁴

Although homopolymers have not found industrial applications, copolymers obtained by an appropriate balance of different monomers are used as intermediates for polyurethanes or as alkyd resins for varnishes and coatings or as hot-melts.

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Additions to C–X Π-Bonds, Part 2

T. Harada , A. Abiko , in Comprehensive Organic Synthesis (Second Edition), 2014

2.10.3.2.2 Malonic acid half thioester

The decarboxylative aldol reaction of malonic acid half thioesters to aldehydes has been developed by Shair and coworkers (equation 23). ⁹³ Treatment of a 1:1 mixture of half thioester 132 and aldehydes with Cu(2-ethylhexanoate)₂ (20   mol%) and 5-methoxybenzimidazole (22   mol%) in wet THF afforded the aldol products 133 in high yield. The asymmetric version of the reaction was realized by using a chiral Cu catalyst system derived from Cu(OTf)₂ (10   mol%) and (R,R)-Phbox 136 (13   mol%) (Scheme 48). ⁹⁴ The reaction was carried out with 2-methylmalonic acid derivative 134 at room temperature to give syn-aldol products 135 diastereo- and enantioselectively. It should be noted that the reaction is compatible with protic functional groups and enolizable aldehydes. In the absence of an aldehyde, decarboxylation of the half thioester was not observed. A mechanistic study revealed that decarboxylation occurs after aldol addition of an enolate derived from the half thioester. ⁹⁵

Scheme 48.

(23) $\text{<mglyph src="https://ars.els-cdn.com/content/image/3-s2.0-B9780080977423002111-fx0200211-14-9780080977423.jpg"></mglyph>}$

Very recently, Shibasaki and coworkers reported a Cu(I)-catalyzed enantioselective decarboxylative aldol-type reaction of β-cyano carboxylic acids (Scheme 49). ⁹⁶ In the presence of a chiral Cu(I) catalyst derived from Cu(OAc) (10   mol%) and TANIAPHOS 121b (10   mol%), 2-cycano-2-phenylpropionic acid (137) reacted with benzaldehyde with liberation of CO₂ to give the aldol-type product 138 in high yield with moderate diastereo- and enantioselectivity. In contrast to the reaction of malonic acid half thioesters, the aldolization step was preceded by the decarboxylation step. It was proposed that the extrusion of CO₂ is facilitated by a soft–soft interaction between Cu(I) and nitrile (139), leading to the generation of Cu(I)-ketenimide 140. The analogous catalytic system was successfully applied to the enantioselective decarboxylative Mannich-type reaction of β-cyano carboxylic acids. ^96,97

Scheme 49.

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TIME ORDER – CHEMICAL OSCILLATIONS

R.P. Rastogi , in Introduction to Non-equilibrium Physical Chemistry, 2008

9.7 Dual control mechanism

Normally, if saccharides are substituted for malonic acid in classical B–Z system, oscillations are observed since Br ⁻–control mechanism operates. This has been ascribed to accumulation of Br⁻ in the system such that [Br⁻] exceeds the critical Br concentration. Critical [Br⁻] is necessary for oscillations to occur [1]. Hence, in order to reduce the prevailing [Br⁻] to the level of [Br₂] critical following steps can be undertaken:

(a)

addition of an additional organic substrate which may get easily brominated [44]; and

(b)

bubbling Br₂ out of the system using an inert gas [45].

Comprehensive studies of the oscillatory features of B–Z reaction involving double substrate such as (i) glucose + acetone; (ii) fructose + acetone; and (iii) sucrose + acetone have been made. One of the interesting features is that the systems display the lower and upper critical limits of [acetone] between which oscillations occurred on increasing [F]. Another significant observation was that beyond a certain [F], oscillations occurred even when no acetone was present in the system. Obviously, at this stage Br⁻-control mechanism is not in operation [46] and an alternative free-radical control mechanism has been suggested [47]. Further studies with B–Z oscillator having (i) fructose + tartaric acid [48]; (ii) fructose + oxalic acid [49]; (iii) xylose + oxalic acid [50]; and (iv) glucose + oxalic acid [51] were performed.

Oscillations in fructose $+{\text{BrO}}_3^{-}+{\text{Ce}}^{+4}+{\mathrm{H}}_2{\text{SO}}_2$ without any bromine scavenger have been observed in the range 0.035–0.7M fructose in a batch reactor as well as CSTR (Fig. 9.9) [46]. Tartaric acid is found to promote oscillations when added to non-oscillation fructose system although no oscillations are observed in tartaric acid $+{\text{BrO}}_3^{-}+{\text{Ce}}^{4+}+{\mathrm{H}}_2{\text{SO}}_4$ system of similar concentration. Within a certain range of fructose concentration, damped complex oscillations are observed in the batch reactor. In CSTR, aperiodic oscillations are observed at higher [F] with decreasing flow rated although sustained periodic oscillations are observed at low (Fig. 9.10) [Fructose].

Figure 9.9. Oscillations in bromide ion potential for the system ${\text{BrO}}_3^{-}$ (0.06M) + Ce⁴⁺(1.45 10⁻³ × M) + H₂SO₄(1.5M) + [Fructose]; (a) 0.02M (b) 0.03M (c) 0.035M (d) 0.04M (e) 0.05M (f) 0.06M (g) 0.07M (h) 0.075M.

Figure 9.10. Oscillations in bromide ion potential in CSTR for the system; Fructose $\left(0.075\mathrm{M}\right)+{\text{BrO}}_3^{-}\left(0.06\mathrm{M}\right)+{\text{Ce}}^{+4}\left(1.45\times {10}^{-3}\times \mathrm{M}\right)+{\mathrm{H}}_2{\text{SO}}_4\left(1.5\mathrm{M}\right)$ at flow rate equal to (a) 0.08 ml/min (b) 2.0 ml/min (c) 2.50 ml/min.

In a particular concentration range, two types of oscillations in Fructose [F]+ acetone oscillator separated by time pause have also been observed in the batch reactor. Oscillations that occur before time pause (first type oscillations are insensitive to addition of Br⁻ up to 10⁻² M and are F + OA similar to that observed in the corresponding fructose oscillator without acetone. On the other hand, oscillations that occur after time pause (second type oscillations) are stopped when [Br⁻] ≈ 10⁻²M. This gives an indication that the first type is non-bromide ion-controlled while the second is Br⁻–controlled. Computer simulation studies confirm that both control mechanisms are operative in the system [46].

Experimental studies on B–Z oscillator having fructose + tartaric acid as double substrate have been undertaken by keeping either of the two organic substrates at a fixed concentration and varying the concentration of the other [48]. A modified mechanism by including following additional steps (7) to (13) in the FKN mechanism has been used to explain the observations.

It may be noted that F, G and OA are not Bromine scavengers. However, acetone acts as a Bromine scavenger. Examination of the above scheme shows that

(a)

Combination of (5) + 2 × (6) yields the autocatalytic reaction for HBrO₂. The inhibiting reactions are (2) and (3). If a proper balance can be maintained between the two, oscillations can occur and the oscillatory reaction would be Br-controlled.

(b)

If combination of (5) and (6) is favoured, autocatalysis of ${\text{BrO}}_2^{•}$ would occur and the corresponding inhibiting reactions would be (7), (8), (12) and (13). Here again if the rates are adjustable, oscillations would occur which will be free-radical controlled.

Oscillatory features of a similar type of B–Z oscillator, Fructose (F) + oxalic acid $[\text{OA}]+{\text{Ce}}^{4+}+{\text{BrO}}_3^{-}+{\mathrm{H}}_2{\text{SO}}_4$ have also been investigated recently [49]. The induction time is found to be usually small or negligible. Both single frequency oscillations and two oscillatory states separated by a time pause are observed. Oscillations occur between two critical limits of [F] and [OA]. Computer simulation correctly predicts some of the oscillatory features such as (i) time of inhibition; (ii) critical limits of [OA]; and (iii) stoppage of oscillation by higher [Br⁻], which conforms the proposed mechanism involving the primary role of Br⁻–control mechanism. The tentative mechanism involves both Br⁻–control and free-radical control mechanism.

Experimental and computational studies on B–Z oscillator with fructose alone as substrate [52] have been recently studied. The phenomena of multiple control mechanism is possible in specific systems. If in a system, number of sets of autocatalytic and inhibitory reaction are present, one can have larger number of control mechanism. To this belongs another example of the B–Z oscillator having double substrate. Thus, oscillations in a B–Z system having oxalic acid (OA) and glucose (G) have been investigated where none of the substrate acts as Br scavenger [51]. Studies have been performed for (i) varying concentration of G while keeping the [OA] fixed; and (ii) varying [OA] but keeping [G] fixed in a batch reactor. In both cases, upper and lower critical limits occur, between which oscillations are observed. Both single and double frequency oscillations have been observed in a wide range of concentration of G as well as of OA. The induction period in most of the cases was < 1 min.

When [G] is fixed and [OA] is varied, the time pause between the sequential oscillations increases with an increase in [OA]. On the other hand, when [OA] is fixed and G is varied, the time pause increases with an increase in [G]. The first-type of oscillations is Br⁻–controlled, where the second is non-Br⁻ controlled. The order of addition of G and OA in the last has no influence on the induction period. However, it influences the oscillatory characteristics. A tentative dual control mechanism has been suggested involving autocatalysis of HBrO₂ and ${\text{BrO}}_2^{•}$ .

The detailed mechanism is as follows:

(1) ${\text{Br}}^{-}+{\text{BrO}}_3^{-}+2{\mathrm{H}}^{+}\rightleftharpoons \text{HOBr}+{\text{HBrO}}_2$

(2) ${\text{Br}}^{-}+{\text{HBrO}}_2+{\mathrm{H}}^{+}\rightleftharpoons 2\text{HOBr}$

(3) ${\text{Br}}^{-}+\text{HOBr}+{\mathrm{H}}^{+}\rightleftharpoons {\text{Br}}_2+{\mathrm{H}}_2\mathrm{O}$

(4) $2{\text{HBrO}}_2\rightleftharpoons \text{HOBr}+{\text{BrO}}_3^{-}+{\mathrm{H}}^{+}$

(5) ${\text{HBrO}}_2+{\text{BrO}}_3^{-}+{\mathrm{H}}^{+}\rightleftharpoons {\text{Br}}_2{\mathrm{O}}_4+{\mathrm{H}}_2\mathrm{O}$

(6) ${\text{Br}}_2{\mathrm{O}}_4\rightleftharpoons 2{\text{BrO}}_2$

(7) ${\text{Ce}}^{3+}+{\text{BrO}}_2^{*}+{\mathrm{H}}^{+}\rightleftharpoons {\text{Ce}}^{4+}+{\text{HBrO}}_2$

which are important steps of FKN mechanism.

The network of reactions around G involves a number of reactions including oxidative products of G i.e.

(8) $\mathrm{G}+{\text{BrO}}_3^{-}+{\mathrm{H}}^{+}\to \mathrm{Q}(\text{gluconic}\text{acid})+{\text{HBrO}}_2$

(9) $\mathrm{G}+\text{HOBr}\to \mathrm{Q}+{\mathrm{H}}^{+}+{\text{Br}}^{-}$

(10) $\mathrm{Q}+{\text{BrO}}_3^{-}+{\mathrm{H}}^{+}\to \mathrm{P}(\text{gluconic}\text{acid})+\text{HOBr}+{\mathrm{H}}_2\mathrm{O}$

(11) $\mathrm{G}+{\text{Br}}_2+{\mathrm{H}}_2\mathrm{O}\to (\text{gluconic}\text{acid})+2{\text{Br}}^{-}+2{\mathrm{H}}^{+}$

(12) $\mathrm{G}+{\text{Ce}}^{4+}\to \mathrm{G}+{\text{Ce}}^{3+}+{\mathrm{H}}^{+}$

(13) $\mathrm{G}+{\text{Ce}}^{4+}+{\mathrm{H}}_2\mathrm{O}\to \mathrm{P}(\text{gluconic}\text{acid})+{\text{Ce}}^{3+}+{\mathrm{H}}^{+}$

The acids P and Q generate free radicals by a one-electron transfer reaction with Ce⁴⁺ as follows:

(14) $\mathrm{Q}+{\text{Ce}}^{4+}\to \mathrm{Q}+{\text{Ce}}^{3+}+{\mathrm{H}}^{+}$

(15) $\mathrm{P}+{\text{Ce}}^{4+}\to \mathrm{P}+{\text{Ce}}^{3+}+{\mathrm{H}}^{+}$

The free radical Q and P can reach with ${\text{BrO}}_2^{•}$ free radical as follows:

(16) $\mathrm{P}+{\text{BrO}}_2^{*}\to \text{product}+{\text{Br}}^{-}+{\mathrm{H}}^{+}$

(17) $\mathrm{Q}+{\text{BrO}}_2^{*}\to \mathrm{P}+\text{HOBr}$

Oxalic acid on the other hand can also undergo the following sequence of reactions:

(18) ${\text{Ce}}^{4+}\text{OA}\to {\text{Ce}}^{3+}+\text{COOH}+{\text{CO}}_2+{\mathrm{H}}^{+}$

(19) ${\text{Ce}}^{4+}+\text{COOH}\to {\text{Ce}}^{3+}+{\mathrm{H}}^{+}+{\text{CO}}_2$

(20) ${\text{BrO}}_2^{•}+\text{COOH}\to {\text{HBrO}}_2+{\text{CO}}_2$

(21) $\text{OA}+{\text{BrO}}_3^{-}+{\mathrm{H}}^{+}\to {\text{HBrO}}_2+2{\text{CO}}_2+{\mathrm{H}}_2\mathrm{O}$

One can also have following type of free-radical recombination reaction:

(22) $2\mathrm{P}\to \text{Product}$

(23) $\mathrm{P}+\mathrm{Q}\to \text{Product}$

(24) $\text{PQ}\to \text{Product}$

Two types of auto catalytic reactions are involved in the above reaction scheme:

(a)

On combing (5), (6) and twice the step of (7), we get

(25) ${\text{HBrO}}_2+{\text{BrO}}_3^{-}+{\text{Ce}}^{3+}+3{\mathrm{H}}^{+}\rightleftharpoons 2{\text{Ce}}^{4+}+{\text{HBrO}}_2+{\mathrm{H}}_2\mathrm{O}$

which leads to autocatalysis of ${\text{HBrO}}_2^{•}$ on the other hand.

(b)

On adding (5), (6) and (7), we get

(26) ${\text{BrO}}_2^{*}+{\text{BrO}}_3^{-}+{\text{Ce}}^{3+}+2{\mathrm{H}}^{+}\rightleftharpoons {\text{Ce}}^{4+}2{\text{BrO}}_2+{\mathrm{H}}_2\mathrm{O}$

which leads to autocatalysis of ${\text{BrO}}_2^{•}$ .

Thus, in the reaction system, there are two processes autocatalysis of (i) HBrO₂; and (ii) ${\text{BrO}}_2^{•}$ . Any species reacting with them can inhibit the whole autocatalytic process. The normal control mechanism in B–Z reaction essentially involves step (25) which is inhibited by Br⁻ according to step (2). This is called Br⁻–control mechanism

The second type of control mechanism involves (i) autocatalysis of ${\text{BrO}}_2^{•}$ step (26); and (ii) inhibitory reactions (16) and (17). This type of mechanism is called free radical control mechanism.

The first one controls the type I oscillations, while the second controls type II as indicated by experiments as well as by computer simulation.

Thus, both the G + OA as well as F + OA oscillators provide examples of dual control mechanism. Multiple-control mechanisms are a distinct possibility.

A simple explanation of dual control mechanism can be easily provided. In the case of type I oscillations, initially in the presence of oxalic acid, a sufficient amount of HBrO₂ is produced, and in turn, by a sequence of reactions Br⁻ is in greater excess than critically needed for balance of positive and negative feedback. However, when G is in excess, free radicals are generated from acid produced by oxidation of G, which reduced the concentration of HBrO₂ and Br⁻. Thus, eventually a situation is reached when the autocatalytic production of HBrO₂ can be balanced by the inhibition through Br⁻. Under such circumstances, the oscillations are Br⁻-controlled

In the case of type II, after a time pause sufficient amount of free radicals are produced via interaction of Ce⁴⁺ with acids produced from the oxidation of glucose. At a certain stage, autocatalytic production of ${\text{BrO}}_2^{•}$ can be balanced by the negative feedback, involving interaction of ${\text{BrO}}_2^{•}$ and P and Q. In course of time, the production of P and Q goes on increasing and when this exceeds the critical concentration necessary for countering the autocatalysis production of ${\text{BrO}}_2^{•}$ , the type II oscillation stops. Thus, two type II oscillations are free-radical controlled (non-Br⁻ controlled).

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Synthesis: Carbon with One Heteroatom Attached by a Multiple Bond

Michael North , in Comprehensive Organic Functional Group Transformations, 1995

3.18.1.1.2 Electrophilic substitutions

Cyanogen chloride reacts with the sodium salts of malonic acid and acetoacetate derivatives to give the cyano derivatives < 1889AC(R)222, 1896CB1171, 1899CB643>. However, use of cyanogen bromide often results in formation of the bromo derivatives instead. Primary aliphatic Grignard reagents also react with cyanogen chloride to give nitriles, but secondary and tertiary Grignard reagents give the corresponding chlorides instead <11CMR(152)388, 12CMR(155)44, 14CMR(158)457, 26BSF1589>. This problem can be overcome by using cyanogen instead of cyanogen chloride, in which case all aliphatic Grignard reagents give nitriles <11MI 318-01, 12MI 318-01, 14MI 318-01, 15AC(R)28, 20AC(R)364>. A wide variety of highly functionalised organozinc compounds have been shown to react with Ts-CN to give the corresponding nitriles with good yields <93TL4623>. Arylisocyanoates <65CB3662> and cyanamides <52CB397> also react with Grignard reagents to give nitriles.

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Find the Concentration of Malon Acid in Each Solution

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