Alkynes tests

The acidic hydrogen in terminal alkynes can readily be replaced by silver, in a diagnostic test. [(Me3P)Ag(C=CPh)] has a polymeric structure while [(Ph3P)Ag(C=CPh)]4 is made of [Ag(PPh3)2]+ and [Ag(C=CPh)2] fragments linked so that the silver atoms form a square [147]. 

Since this scheme regenerates the original coordinatively unsaturated Ti+2 centers upon desorption of the aromatic, it could, in principle, represent a catalytic cycle for heterogeneous alkyne cyclization. The present study reports a test of that h3T>othesis—the feasibility of catal5hic cyclotrimerization—on a reduced Ti02 surface in UHV. 

Rapid decolorization of Br2/CCl4 is a test for alkenes and alkynes. 

A variety of triazole-based monophosphines (ClickPhos) 141 have been prepared via efficient 1,3-dipolar cycloaddition of readily available azides and acetylenes and their palladium complexes provided excellent yields in the amination reactions and Suzuki-Miyaura coupling reactions of unactivated aryl chlorides <06JOC3928>. A novel P,N-type ligand family (ClickPhine) is easily accessible using the Cu(I)-catalyzed azide-alkyne cycloaddition reaction and was tested in palladium-catalyzed allylic alkylation reactions <06OL3227>. Novel chiral ligands, (S)-(+)-l-substituted aryl-4-(l-phenyl) ethylformamido-5-amino-1,2,3-triazoles 142,... 

A simple test to distinguish between 2-pentene and cyclopentane is to add a few drops of a red Br2 solution to the unknown liquid. The reddish color will disappear if the liquid is an alkene or alkyne, e.g., 2-pentene, due to the addition of Br2 to the multiple bond. No such addition reaction occurs between Br2 and cyclopentane. 

Addition reactions form the basis for tests that distinguish alkenes and alkynes from alkanes. Bromine, Br2, has a deep reddish-brown colour. When bromine is added to an alkene or alkyne, an addition reaction takes place. As the bromine is used up, the brown colour of the bromine disappears. Since alkanes cannot undergo addition reactions, no reaction takes place when bromine is added to an alkane. 

The substituents on the alkyne and the cyano components can be widely varied so that we have been able to develop the basic reaction of Eq.(l) into a general synthetic method for preparing pyridines (see Section III). We have concentrated on the development of highly reactive organoco-balt(I) complexes and have tested a number of catalyst complexes under standard conditions. Both the influence of the controlling ligand Y and the neutral ligand L on the catalytic turnover number (TON) have been determined. The final step involves the optimization of the reaction conditions. 

After extensive screening of various aldehydes to optimize the reaction conditions, it was found that aromatic aldehydes were able to serve as a carbon monoxide source, in which the electronic nature of the aldehydes is responsible for their ability to transfer CO efficiently [24]. Consequently, aldehydes bearing electron-withdrawing substituents are more effective than those bearing electron-donating substituents, with pentafluoro-benzaldehyde providing optimal reactivity. Interestingly, for all substrates tested the reaction is void of any complications from hydroacylation of either the alkene or alkyne of the enyne. Iridium and ruthenium complexes, which are known to decarboxylate aldehydes and catalyze the PK reaction, demonstrated inferior efficiency as compared to... 

Complex 93 was tested in a variety of [5+2] cycloaddition reactions and compared, where relevant, with some other effective catalysts (Tab. 13.6). Excellent results were obtained with VCPs tethered to terminal and internal alkynes, alkynoates, and aUcenes. 

The negative test for a 1-alkyne with Ag establishes the second structure, 4-methyI-2-pentyne. 

Heavy metal acetylides test for terminal alkynes... 

Reaction of an alkene with hot basic potassium permanganate (KMn04) results in cleavage of the double bond, and formation of highly oxidized carbons. Therefore, unsubstituted carbon atoms become CO2, mono-substituted carbon atoms become carboxylates, and di-substituted carbon atoms become ketones. This can be used as a chemical test (known as the Baeyer test) for alkenes and alkynes, in which the purple colour of the KMn04 disappears, and a brown Mn02 residue is formed. 

In the case of internal symmetric or terminal alkynes, reaction takes place according to Markovnikov selectivity, unlike the problem of regioselectivity that appears when internal asymmetric alkynes are used. Unfortunately, at that time only the gold(I) compound K[Au(CN)2] was tested, a compound that is now known not to be effective as a catalyst, unlike many other gold(I) compounds. 

Until 1998, only gold(III) was believed to be effective for catalyzing these processes because, as mentioned previously, only the gold(I) compound K[Au (CN)2] was tested and it was inert to catalysis. Fortunately, Teles et al. reported very strong activity in the addition of alcohols to alkynes when they used cationic gold( I) -phosphane complexes [14]. In this study, the aforementioned authors tested for the first time the suitability of nucleophilic carbenes that displayed even greater activity than other gold complexes, but they were unable to synthesize the subsequent cationic derivatives. 

The impressive activity achieved by Teles catalyst was improved some years later by the use of CO as an additive [92]. In this study, Hayashi and Tanaka reported a TOF of 15600h 1, at least two orders of magnitude higher than [as-PtCl2(tppts)2], for the hydration of alkynes, providing an alternative synthetic route to the Wacker oxidation. Although several solvents were tested, the best results were obtained with aqueous methanol, and sulfuric acid or HTfO as acidic promoters. Unlike Utimoto s observation, in this case terminal propargylic alcohols partially (17-20%) delivered anti-Markovnikov product, in addition to the Markovnikov species. Some years before, Wakatsuki et al. had already reported the anti-Markovnikov hydration of terminal alkynes catalyzed by ruthenium(II) [93]. 

In a joint study by Schmidbaur and Raubenheimer, several phosphine carboxylates and sulfonates of gold and silver were tested as catalysts for the hydration of nonactive alkynes [99]. While the gold complexes showed high activity for these reactions, analogous silver (I) complexes were not active in them. This different behavior was due to the fact that gold cations are weaker acceptors for their ligands and counterions than silver (I) cations (Figure 8.3). 

Figure 8.3 Cold complexes tested for the hydration of non-active alkynes.

Indenyl ethers were synthesized via intramolecular carboalkoxylation of alkynes. In this process, a benzylic ether group played a nucleophile role to capture a vinyl gold intermediate obtained by alkyne activation. The first catalytic system tested by Toste and Dube in this study was a mixture of [AuClPPh3] and AgBF4. However, the moderate yield prompted them to research the use of more electrophilic gold(I) complexes such as [AuP(p-CF3-C6H4)3]BF4, which increased the yield of cydized products by 70% [107]. 

At the time, these suggestions could not be tested as silacyclopropenes were unknown, but an alternative mechanism was proposed involving the initial formation of the 1,2-disilacyclobutene, which ring opens to the 1,4-disilabuta-l,3-diene reversibly to add a second molecule of alkyne. The disilacyclobutene (27), formed from 2-butyne, adds 3-hexyne to give the disilin (28 Scheme 37) (76JA7746). 

The acidity of the terminal hydrogen in 1-alkynes provides a simple and useful test for 1-alkynes. With silver-ammonia solution (AgNOs in aqueous ammonia), 1-alkynes give insoluble silver salts, whereas disubstituted alkynes do not ... 

Electrophilic addition of the halogens and related X—Y reagents to alkenes and alkynes has been a standard procedure since the beginning of modem organic chemistry.1 Anti electrophilic bromination of such simple compounds as cyclohexene and ( )- and (Z)-2-butene, and variants of this reaction when water or methanol are solvents (formation of halohydrin or their methyl ethers, respectively), are frequently employed as prototype examples of stereospecific reactions in elementary courses in organic chemistry. A simple test for unsaturation involves addition of a dilute solution of bromine in CCU to the... 

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