As well as this variety of oxidation states, sulfur shows a sometimes-surprising versatility in function. Simple S(II) compounds are good nucleophiles, as you would expect from the high-energy non-bonding lone pairs (3sp³) rather than the 2sp³ of oxygen). A mixture of a thiol (RSH, the sulfur equivalent of an alcohol) and NaOH reacts with an alkyl halide to give the sulfide alone by nucleophilic attack of RS⁻.

Thiols (RSH) are more acidic than alcohols so the first step is a rapid proton exchange between the thiol and hydroxide ion. The thiolate anion then carries out a very efficient SN₂ displacement on the alkyl bromide to give the sulfide. Notice that the thiolate anion does not attack the carbonyl group. Small basic oxyanions have high charge density and low energy fi lled orbitals—they are hard nucleophiles that prefer to attack protons and carbonyl groups. Large, less basic thiolate anions have high-energy fi lled orbitals and are soft nucleophiles. They prefer to attack saturated carbon atoms. Thiols and thiolates are good soft nucleophiles.

●Thiols (RSH) are more acidic than alcohols (ROH) but sulfur compounds are better nucleophiles than oxygen compounds towards saturated carbon atoms (SN₂).

They are also good soft electrophiles. Sulfenyl chlorides (RSCl) are easily made from disulfides (RS–SR) and sulfuryl chloride (SO2Cl₂). This S(VI) chloride has electrophilic chlorine atoms and is attacked by the nucleophilic disulfide to give two molecules of RSCl and gaseous SO₂. There’s a lot of sulfur chemistry here! We start with a nucleophilic attack by one sulfur atom of the disulfide. The intermediate contains a tricoordinate sulfur cat ion or sulfonium salt. The chloride ion now attacks the other sulfur atom of this intermediate and two molecules of RSCl result. Each atom of the original disulfide has formed an S–Cl bond. One sulfur atom was a nucleophile towards chlorine and the other an electrophile.

The product of this reaction, the sulfenyl chloride, is also a good soft electrophile towards carbon atoms, particularly towards alkenes. The reaction is very like bromination, with a three-membered cyclic sulfonium ion intermediate replacing. The reaction is stereospecific and the product is anti.

At higher oxidation states the compounds become harder electrophiles as the positive charge on sulfur increases. We have already mentioned tosyl (para-toluenesulfonyl) chloride, TsCl, as an electrophile for alkoxide ions in this chapter and in earlier chapters. At this higher oxidation state it might seem unlikely that sulfur could also be a good nucleophile, but consider the result of reacting TsCl with zinc metal. Zinc provides two electrons and turns the compound into an anion. This anion can also be drawn in two ways.

Surprisingly, this anion is also a good soft nucleophile and attacks saturated carbon atoms through the sulfur atom. In this case attack occurs at the less substituted end of an allylic bromide to give an allylic sulfone, which we will use later on.

اخر الاخبار

اخبار العتبة العباسية المقدسة

عباس.. طفل فقد والده فوجد في خدمة زائري عاشوراء وطنًا آمنًا

شعبة الخطابة النسوية تواصل إقامة مجالس العزاء في شهر المحرم الحرام

لليوم الخامس.. العتبة العباسية المقدسة تقيم مجلس عزاء في صحن مرقد أبي الفضل العباس (عليه السلام)

قسم الشؤون الفكرية يقيم مجلس عزاء حسيني في العاصمة التنزانية دار السلام

المزيد

الآخبار الصحية

لمن تجاوز الستين.. عليك بشرب 4 أكواب من القهوة يوميا ؟

الحليب مع العسل.. مزيج يمنحك 7 فوائد صحية

لا تبالغ في التنظيف.. قليل من "الاتساخ" قد يحمي عائلتك

دراسة تكشف علاقة خطيرة بين عمر الأم وصحة مولودها

المزيد

الآخبار التكنلوجية

هل هاتفك مراقب؟.. 5 علامات خطيرة تكشف التجسس عليك

دبي تطلق أول رحلة تجريبية للتاكسي الجوي

كيف تساعد الصيانة الوقائية في الحفاظ على كفاءة التكييف في سيارتك ؟

في ظاهرة غريبة حيرت العلماء.. كوكبنا قد يسجل أقصر يوم في التاريخ هذا الصيف!

المزيد

مواضيع ذات صلة

Sulfur-stabilized anions

Symmetry in intramolecular crossed Claisen condensations

Intramolecular crossed Claisen ester condensations

Crossed Claisen ester condensations between two different esters

Directed C-acylation of esters

Claisen condensations between ketones and esters

Reactive esters that cannot enolize

The Claisen ester condensation and other self-condensations

Problems with acylation at carbon

Cross-condensations

The aldol reaction

Nitroalkanes are superb nucleophiles for conjugate addition