Iodine in methanol

For commercially pure titanium, the specific environments to be avoided are pure methanol and red, fuming nitric acid " , although in both environments the presence of 2% of water will inhibit cracking. On the other hand, the presence of either bromine or iodine in methanol aggravates the effect. When it does occur, stress-corrosion cracking of commercially pure titanium is usually intergranular in habit. 

Stereoselective syntheses of trisubstituted alkenes are based on E- and Z-alkenyldioxaborinanes. Reaction with an alkyllithium reagent forms an ate adduct that rearranges on treatment with iodine in methanol.31... 

The reaction of nitrones of the 3-imidazoline series (295) with bromine and amyl nitrite, in the presence of base, gives a-tribromomethyl-(296) and a-hydroxyaminomethyl derivatives (297) (538). Bromination of nitrones (295) with N -bromosuccinimide (NBS) in CCI4 or bromine in methanol leads to the formation of a-bromoalkyl (298 a,b, Hal = Br) and a-dibromomethyl (299) nitrones (539-541). The reaction with iodine in methanol gives the mono iodo derivative (300) (541). The reaction with A-chlorosuccinimide (NCS) in CCI4 leads to a-chloroethyl nitrones (298b, Hal = Cl) and a,a-dichloromethyl nitrones (301) (Scheme 2.118) (225). 

In the volumetric method, the titrant can be a solution of iodine, methanol, sulfur dioxide, and an organic base, as described previously. Such a mixture is commonly known as the Karl Fischer reagent and can be purchased from any chemical vendor. It can also be a solution of iodine in methanol solvent. In that case, a Karl Fischer solvent containing the other required components is needed for the titration vessel. 

For iodine in methanol solution, the partial molar volume of the solute is essentially constant, independent of concentration, and is equal to 62.3 cm ... 

Because of the polyfunctional nature of carbohydrates, protective-group strategy plays an important role in synthetic methodology involving this class of compounds. In the present Chapter, results are described from a study of the utility of N-trimethylsilyl- and N-tert-butyldimethylsilyl-phthalimide for the selective silylation of primary hydroxyl groups in carbohydrates. Also described, is a new, facile method for cleavage of acetals and dithioacetals in carbohydrate derivatives the method involves treatment of the derivatives with a dilute solution of iodine in methanol. 

Cleavage of Acetals and Dithioacetals in Carbohydrate Derivatives Using Iodine in Methanol... 

We present a preliminary study on the structural dynamics of photo-excited iodine in methanol. At early time delays after dissociation, 1 - 10 ns, the change in the diffracted intensity AS(q, t) is oscillatory and the high-q part 4 -8 A 1 is assigned to free iodine atoms. At later times, 10-100 ns, expansive motion is seen in the bulk liquid. The expansion is driven by energy released from the recombination of iodine atoms. The AS(q, t) curves between 0.1 and 5 (is coincide with the temperature differential dS/dT for static methanol with a temperature rise of 2.5 K. However, this temperature is five times greater than the temperature deduced from the energy of dissociated atoms at 1 ns. The discrepancy is ascribed to a short-lived state that recombines on the sub-nanosecond time scale. 

Fig. 4. The diffraction pattern from the ground state of iodine in methanol is shown on the right. The beamstop is seen as a dark circular area in the centre and the bright ring is the correlation peak from the liquid. The picture on the right is the subtraction of the ground state from the 100 ps frame. Note the black ring around the beamstop. That is the signature of dissociation.

Fig. 6. The q-integrated photosignal of iodine in methanol from a time-slicing experiment. The red curve is the temporal profile of the x-ray pulse.

Orthoamide 123 cleanly reduced mercuric acetate in ethanol at 25°C to mercury or mercurous acetate. The organic product formed is guanidinium salt 129 lX= OAc). Similarly, iodine in methanolic potassium carbonate at 25°C oxidized orthoamide 123 to guanidinium iodide 129 (X= I). On the other hand, orthoamide 122 does not react with mercuric acetate even in boiling ethanol. Syn-elimination of mercury and acetic acid from complex 130 must be slow but anti-elimination from complex 131 (Y= l or HgX2) must occur readily. 

Ketones, R-CH2COCH2-R, undergo Z-selective oxidation to give useful acrylates (85), using KOH and molecular iodine in methanol.325 Evidence for the formation ( ) of an , ,-diiodokct.onc intermediate is presented, followed by a Favorskii-type rearrangement. 

The use of a 1% solution of iodine in methanol at 40 °C has been reported to effect the cleavage of trityl and dimethoxytrityl ethers.206 Again, the ability of solutions of iodine in methanol to release of small amounts of HI into the reaction mixture was credited. In order to further examine the role of acid in the deprotection, a variety of bases were added to the reaction mixture. In the... 

Some Examples of the Installation and Removal of Cyclic Acetals Using Iodine-in-methanol Starting Material Product Reagents Yield Ref. 

Tetrahydropyranyl (THP) ethers, another species known to be unstable to acid, have similarly been reported to be cleaved by solutions of iodine in methanol.209 At room temperature, cleavage of the THP ethers was complete in 1.5 to 8 h. As with the previous example using iodine in methanol at lower than reflux temperature, TBDMS ethers were stable to these conditions. The ability to tune the reactivity of the iodine in methanol system by simply controlling the temperature is of value in selective deprotection. This is even more useful when fluorine, known to remove only silyl ethers,105 is exploited. Given that methoxymethyl ethers, essentially acetals, are known to be cleaved under acidic conditions, it seems likely they too should be subject to removal by solutions of iodine in methanol. Sundry examples of deprotections using iodine in methanol are presented in Table IV. 

The cleavage of acetals with catalytic iodine in methanol is a reaction first reported by Walter Szarek and co-workers6 in the 1980s. Although a mechanism has never been proposed in the literature, it is conceivable that the C(l)-exo-acetal oxygen of 10 could attack iodine to form 25 and iodide ion (Scheme 12.8). Loss of the C(l)-0-substituent could then occur to create 26, which could capture iodide ion and methanol to form 27 and acetone. Such a mechanism would regenerate the catalytic quantity of iodine needed to propagate the catalytic cycle. 

Phenols — quinones. Oxidation of phenols to quinones can be effected with 1 eq. of H202 (60%) and excess iodine in methanol at room temperature. Yields are generally 70-98%. The actual oxidant is probably iodine and the function of... 

The methyl esters prepared by oxidation of 96 and 97, respectively, with iodine in methanolic potassium hydroxide were converted into atropine-like drugs by transesterification with 2-(dimethylamino)-... 

Treatment of iodoalkynes with indium and iodine in methanol promotes a reductive 5-i jcti-cyclization to furnish bicyclic vinylidene tetrahydrofurans in good yields (Equation 95) <2002TL4585>. 

Benzylidene acetals are frequently used for the protection of the 4- and 6-hydroxyl groups of pyranoses, Reclamation of the diol can be accomplished by many methods that will be discussed below, but Scheme 3.53 shows an unusual cleavage of benzylidene acetals protecting the glucose moieties in 53.1 using 1% iodine in methanol (w/v),86 The reaction works equally well with isopropylidene, ethylidene and dithioacetals,87... 

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