Sigma-Aldrich Corporation 3.375% Notes due November 1, 2020

Exhibit 4.2

THIS GLOBAL NOTE IS HELD BY THE DEPOSITARY (AS DEFINED IN THE INDENTURE GOVERNING THIS NOTE) OR ITS NOMINEE IN CUSTODY FOR THE BENEFIT OF THE BENEFICIAL OWNERS HEREOF, AND IS NOT TRANSFERABLE TO ANY PERSON UNDER ANY CIRCUMSTANCES EXCEPT THAT (1) THIS GLOBAL NOTE MAY BE EXCHANGED OR TRANSFERRED AS PROVIDED IN THE INDENTURE, (2) THIS GLOBAL NOTE MAY BE DELIVERED TO THE TRUSTEE FOR CANCELLATION PURSUANT TO SECTION 3.8 OF THE INDENTURE AND (3) THIS GLOBAL NOTE MAY BE TRANSFERRED TO A SUCCESSOR DEPOSITARY WITH THE PRIOR WRITTEN CONSENT OF THE COMPANY.

UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY, A NEW YORK CORPORATION (“DTC”), TO THE COMPANY OR ITS AGENT FOR REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT, AND ANY CERTIFICATE ISSUED IS REGISTERED IN THE NAME OF CEDE & CO. OR SUCH OTHER NAME AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC (AND ANY PAYMENT IS MADE TO CEDE & CO. OR SUCH OTHER ENTITY AS IS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF DTC), ANY TRANSFER, PLEDGE, OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON IS WRONGFUL INASMUCH AS THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST HEREIN.

CUSIP: 826552 AA9

Sigma-Aldrich Corporation

3.375% Notes due November 1, 2020

Sigma-Aldrich Corporation., a Delaware corporation (the “Company”, which term includes any successor under the Indenture hereinafter referred to), for value received, promises to pay to CEDE & CO., or its registered assigns, the principal sum of THREE HUNDRED MILLION DOLLARS ($300,000,000), or such other amount as indicated on the Schedule of Exchange of Notes attached hereto, on November 1, 2020.

1. Principal and Interest.

The Company promises to pay the principal of this Note on November 1, 2020.

The Company promises to pay interest on the principal amount of this Note on each interest payment date, as set forth on the face of this Note, at the rate of 3.375% per annum.

Interest will be payable semiannually (to the Holders of record of the Notes at the close of business on April 15 or October 15 immediately preceding the interest payment date) on each interest payment date, commencing May 1, 2011.

Interest on this Note will accrue from the most recent date to which interest has been paid on this Note (or, if there is no existing default in the payment of interest and if this Note is authenticated between a regular record date and the next interest payment date, from such interest payment date) or, if no interest has been paid, from October 28, 2010 (the “Issue Date”). Interest will be computed on the basis of a 360-day year of twelve 30-day months.

The Company will pay interest on overdue principal, premium, if any, and, to the extent lawful, interest at the rate per annum applicable to this Note. Interest not paid when due and any interest on principal, premium or interest not paid when due will be paid to the Persons that are Holders on a Special Record Date, which will be the 15th day preceding the date fixed by the Trustee for the payment of such interest, whether or not such day is a Business Day. At least 15 days before a Special Record Date, the Trustee, in the name and at the expense of the Company, will send to each Holder a notice that sets forth the Special Record Date, the payment date and the amount of interest to be paid.

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2. Indenture.

This is one of the Notes issued as a series of Debt Securities under an Indenture dated as of October 28, 2010 (as further amended from time to time, the “Indenture”), between the Company and Deutsche Bank Trust Company Americas, as Trustee. Capitalized terms used herein are used as defined in the Indenture unless otherwise indicated. The terms of the Notes include those stated in the Indenture and the Officers’ Certificate setting forth the form and the terms of the Notes and those made part of the Indenture by reference to the Trust Indenture Act. The Notes are subject to all such terms, and Holders are referred to the Indenture and the Trust Indenture Act for a statement of all such terms. To the extent permitted by applicable law, in the event of any inconsistency between the terms of this Note and the terms of the Indenture, the terms of the Indenture will control.

The Notes are general unsecured obligations of the Company. The Officer’s Certificate limits the initial aggregate principal amount of the Notes to $300,000,000, but the Company may “re-open” the notes and, subject to certain tax limitations, issue additional Notes on terms identical in all respects to the initial Notes (except for the date of issuance, the date interest begins to accrue and, in certain circumstances, the first interest payment date).

3. Redemption and Repurchase; Discharge Prior to Redemption or Maturity.

The Notes will be redeemable, in whole or from time to time in part, at the Company’s option on any date (a “Redemption Date”), at a redemption price equal to the greater of: (a) 100% of the principal amount of the Notes to be redeemed; or (b) the sum of the present values of the remaining scheduled payments of principal and interest on the Notes to be redeemed (exclusive of interest accrued to the Redemption Date) from the Redemption Date through the Stated Maturity of the Notes being redeemed, in each case discounted to the Redemption Date on a semi-annual basis (assuming a 360-day year consisting of twelve 30-day months) at the Treasury Rate (as defined below) plus 15 basis points.

At any time on or after three months prior to the Stated Maturity, the Notes will be redeemable as a whole or in part, at the Company’s option on the Redemption Date, at a redemption price equal to 100% of the principal amount of the Notes to be redeemed plus accrued and unpaid interest on the Notes to be redeemed to the Redemption Date.

In each case, the Company will pay accrued and unpaid interest on the principal amount being redeemed to the Redemption Date.

“Treasury Rate” means, with respect to any Redemption Date, the rate per year equal to: (1) the yield, under the heading which represents the average for the immediately preceding week, appearing in the most recently published statistical release designated “H.15(519)” or any successor publication which is published weekly by the Board of Governors of the Federal Reserve System and which establishes yields on actively traded United States Treasury securities adjusted to constant maturity under the caption “Treasury Constant Maturities,” for the maturity corresponding to the applicable Comparable Treasury Issue; provided that, if no maturity is within three months before or after the remaining term of the Notes to be redeemed, yields for the two published maturities most closely corresponding to the applicable Comparable Treasury Issue shall be determined and the Treasury Rate shall be interpolated or extrapolated from those yields on a straight line basis, rounding to the nearest month; or (2) if such release (or any successor release) is not published during the week preceding the calculation date or does not contain such yields, the rate per year equal to the semi-annual equivalent yield to maturity of the applicable Comparable Treasury Issue, calculated using a price for the applicable Comparable Treasury Issue (expressed as a percentage of its principal amount) equal to the Comparable Treasury Price for that Redemption Date.

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“Comparable Treasury Issue” means the United States Treasury security selected by the Quotation Agent that would be utilized, at the time of selection and in accordance with customary financial practice, in pricing new issues of corporate debt securities of comparable maturity to the remaining term of the Notes.

“Comparable Treasury Price” means, with respect to any Redemption Date, (1) the average of three Reference Treasury Dealer Quotations for the Redemption Date, after excluding the highest and lowest Reference Treasury Dealer Quotations or (2) if the Quotation Agent obtains fewer than four Reference Treasury Dealer Quotations, the average of all such Reference Treasury Dealer Quotations.

“Quotation Agent” means one of the Reference Treasury Dealers appointed by the Company as Quotation Agent.

“Reference Treasury Dealer” means (1) each of Banc of America Securities LLC and J.P. Morgan Securities LLC and their respective successors, unless any of them ceases to be a primary U.S. Government securities dealer in New York City (a “Primary Treasury Dealer”), in which case the Company shall substitute another Primary Treasury Dealer and (2) any other Primary Treasury Dealer the Company selects.

“Reference Treasury Dealer Quotations” means, with respect to each Reference Treasury Dealer and any Redemption Date, the average, as determined by the Quotation Agent of the bid and asked prices for the Comparable Treasury Issue (expressed in each case as a percentage of its principal amount) quoted in writing to the Quotation Agent by that Reference Treasury Dealer at 5:00 P.M., New York City time, on the third Business Day preceding that Redemption Date.

Notice of redemption will be mailed at least 30 but not more than 60 days before the Redemption Date to each Holder of record of the Notes to be redeemed at its registered address. If less than all of the Notes are to be redeemed at any time, the Trustee will select Notes to be redeemed on a pro rata basis, by lot, or by any other method the Trustee deems fair and appropriate. The notice of redemption for the Notes will state, among other things, the amount of Notes to be redeemed, the Redemption Date, the manner in which the redemption price will be calculated and the place or places that payment will be made upon presentation and surrender of Notes to be redeemed. Unless the Company defaults in the payment of the redemption price, interest will cease to accrue on any Notes that have been called for redemption at the Redemption Date.

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Unless the Company has exercised its right to redeem the Notes described above, upon the occurrence of a Change of Control Triggering Event, each Holder of Notes shall have the right to require the Company to repurchase all or any part of that Holder’s Notes pursuant to an offer by the Company (a “Change of Control Offer”) at an offer price equal to 101% of the aggregate principal amount thereof plus accrued and unpaid interest, if any, thereon, up to, but not including, the date of purchase, subject to the rights of holders of notes on the relevant record date to receive interest due and owing on the relevant interest payment date. Unless the Company has exercised its right to redeem the Notes described above, within 30 days following the date upon which the Change of Control Triggering Event occurs or, at the Company’s option, prior to any Change of Control but after the public announcement of the pending Change of Control, the Company will be required to send, by first class mail, a notice to each Holder of Notes to their addresses as set forth in the Security Register, with a copy to the Trustee, which notice will govern the terms of the Change of Control Offer. Such notice will state, among other things, the purchase date, which must be no earlier than 30 days nor later than 60 days from the date such notice is mailed, other than as may be required by law (the “Change of Control Payment Date”). The notice, if mailed prior to the date of consummation of the Change of Control, will state that the Change of Control Offer is conditioned on the Change of Control being consummated on or prior to the Change of Control Payment Date.

On the Change of Control Payment Date, the Company will, to the extent lawful: (i) accept or cause a third party to accept for payment all Notes or portions of Notes properly tendered pursuant to the Change of Control Offer; (ii) deposit or cause a third party to deposit with the Paying Agent an amount equal to the Change of Control Payment in respect of all Notes or portions of Notes properly tendered; and (iii) deliver or cause to be delivered to the Trustee the Notes properly accepted together with an Officer’s Certificate stating the aggregate principal amount of Notes or portions of Notes being repurchased.

The Company will not be required to make a Change of Control Offer with respect to the Notes if a third party makes such an offer in the manner, at the times and otherwise in compliance with the requirements for such an offer made by the Company and such third party purchases all the Notes properly tendered and not withdrawn under its offer. In addition, the Company will not repurchase any Notes if there has occurred and is continuing on the Change of Control Payment Date an Event of Default under the Indenture, other than a default in the payment of the Change of Control Payment on the Change of Control Payment Date.

The Company must comply in all material respects with the requirements of Rule 14e-1 under the Securities Exchange Act of 1934, as amended (the “Exchange Act”), and any other securities laws and regulations thereunder to the extent those laws and regulations are applicable in connection with the repurchase of the Notes as a result of a Change of Control Triggering Event. To the extent that the provisions of any such securities laws or regulations conflict with the Change of Control Offer provisions of the Notes, the Company will be required to comply with those securities laws and regulations and will not be deemed to have breached its obligations under the Change of Control Offer provisions of the Notes by virtue of any such conflict.

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For purposes of the foregoing Change of Control Offer provisions, the following definitions are applicable:

“Change of Control” means the occurrence of any of the following after the Issue Date: (1) the direct or indirect sale, lease, transfer, conveyance or other disposition (other than by way of merger or consolidation), in one or a series of related transactions, of all or substantially all of the Company’s assets and the assets of the Company’s Subsidiaries taken as a whole to any “person” or “group” (as those terms are used in Section 13(d)(3) of the Exchange Act) other than to the Company or one of its Subsidiaries; (2) the consummation of any transaction (including, without limitation, any merger or consolidation) the result of which is that any “person” or “group” (as those terms are used in Section 13(d)(3) of the Exchange Act) (other than the Company or one of its Subsidiaries) becomes the “beneficial owner” (as defined in Rules 13d-3 and 13d-5 under the Exchange Act), directly or indirectly, of the Company’s Voting Stock representing a majority of the voting power of the Company’s outstanding Voting Stock; (3) the Company consolidates with, or merges with or into, any Person, or any Person consolidates with, or merges with or into, the Company, in any such event pursuant to a transaction in which any of the Company’s outstanding Voting Stock or Voting Stock of such other Person is converted into or exchanged for cash, securities or other property, other than any such transaction where the Company’s Voting Stock outstanding immediately prior to such transaction constitutes, or is converted into or exchanged for, Voting Stock representing a majority of the voting power of the Voting Stock of the surviving Person immediately after giving effect to such transaction; (4) the first day on which the majority of the members of the Company’s Board of Directors cease to be Continuing Directors; or (5) the adoption by the Company’s stockholders of a plan relating to the Company’s liquidation or dissolution.

Notwithstanding the foregoing, a transaction (or series of related transactions) will not be deemed to involve a Change of Control under clause (2) above if (i) the Company becomes a direct or indirect wholly-owned subsidiary of a holding company and (ii)(A) the direct or indirect holders of the Voting Stock of such holding company immediately following that transaction are substantially the same as the Holders of the Company’s Voting Stock immediately prior to that transaction or (B) immediately following that transaction no person or group (as those terms are used in Section 13(d)(3) of the Exchange Act) (other than a holding company satisfying the requirements of this sentence) is the beneficial owner, directly or indirectly, of more than 50% of the Voting Stock of such holding company.

“Change of Control Triggering Event” means, with respect to the Notes, (i) the rating of the Notes is lowered by each of the Rating Agencies on any date during the period (the “Trigger Period”) commencing on the earlier of (a) the occurrence of a Change of Control and (b) the first public announcement by the Company of any Change of Control (or pending Change of Control), and ending 60 days following consummation of such Change of Control (which Trigger Period will be extended following consummation of a Change of Control for so long as any of the Rating Agencies has publicly announced that it is considering a possible ratings change), and (ii) the Notes are rated below Investment Grade by each of the Rating Agencies on any day during the Trigger Period; provided that a Change of Control Trigger Event will not be deemed to have occurred in respect of a particular Change of Control if each Rating Agency making the reduction in rating does not publicly announce or confirm or inform the Trustee at the Company’s or the Trustee’s request that the reduction was the result, in whole or in part, of any event or circumstance comprised of or arising as a result of, or in respect of, the Change of Control.

Notwithstanding the foregoing, no Change of Control Triggering Event will be deemed to have occurred in connection with any particular Change of Control unless and until such Change of Control has actually been consummated.

“Continuing Director” means, as of any date of determination, any member of the Company’s Board of Directors who: (1) was a member of the Company’s Board of Directors on the Issue Date; or (2) was nominated for election or elected or appointed to the Company’s Board of Directors with the approval of a majority of the Continuing Directors who were members of the Company’s Board of Directors at the time of such nomination, election or appointment (or such lesser number comprising a majority of a nominating committee if authority for such nomination, election or appointment has been delegated to a nominating committee whose authority and composition have been approved by at least a majority of the directors who were Continuing Directors at the time such committee was formed) either by a specific vote or by approval of the Company’s proxy statement in which such member was named as a nominee for election as a director, without objection to such nomination or otherwise.

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Holders would not be entitled to require the Company to purchase the Notes in certain circumstances involving a significant change in the composition of the Company’s Board of Directors, including in connection with a proxy contest where the Company’s Board of Directors does not approve a dissident slate of directors but approves them as Continuing Directors, even if the Company’s Board of Directors initially opposed the directors.

“Investment Grade” means a rating of Baa3 or better by Moody’s (or its equivalent under any successor rating category of Moody’s) and a rating of BBB- or better by S&P (or its equivalent under any successor rating category of S&P), and the equivalent investment grade credit rating from any replacement rating agency or rating agencies selected by the Company under the circumstances permitting the Company to select a replacement rating agency and in the manner for selecting a replacement rating agency, in each case as set forth in the definition of “Rating Agency.”

“Moody’s” means Moody’s Investors Service, Inc., a subsidiary of Moody’s Corporation, and its successors.

“Person” means any individual, corporation, partnership, limited liability company, business trust, association, joint-stock company, joint venture, trust, incorporated or unincorporated organization or government or any agency or political subdivision thereof.

“Rating Agency” means each of Moody’s and S&P; provided, that if any of Moody’s or S&P ceases to provide rating services to issuers or investors, the Company may appoint another “nationally recognized statistical rating organization” within the meaning of Rule 15c3-1(c)(2)(vi)(F) under the Exchange Act as a replacement for such Rating Agency; provided that the Company shall give notice of such appointment to the Trustee.

“S&P” means Standard & Poor’s Ratings Services, a division of The McGraw-Hill Companies, Inc., and its successors.

“Voting Stock” of any specified Person as of any date means the capital stock of such Person that is at the time entitled to vote generally in the election of the board of directors of such Person.

There is no sinking fund applicable to the Notes.

The provisions of Articles XII and XV of the Indenture shall be applicable to the Notes.

4. Registered Form; Denominations; Transfer; Exchange.

The Notes are in registered form without coupons in minimum denominations of $2,000 principal amount and any multiple of $1,000 in excess thereof. A Holder may register the transfer or exchange of Notes in accordance with the Indenture. The Trustee may require a Holder to furnish appropriate endorsements and transfer documents and to pay any taxes and fees required by law or permitted by the Indenture.

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5. Defaults and Remedies.

If an Event of Default, as defined in the Indenture, occurs and is continuing, the Trustee or the Holders of at least 25% in principal amount of the Notes may declare all the Notes to be due and payable. If a bankruptcy or insolvency default with respect to the Company or a Restricted Subsidiary occurs as provided in the Indenture and is continuing, the Notes automatically become due and payable. Holders may not enforce the Indenture or the Notes except as provided in the Indenture. The Trustee may require indemnity or security satisfactory to it before it enforces the Indenture or the Notes. Subject to certain limitations, Holders of a majority in principal amount of the Notes then outstanding may direct the Trustee in its exercise of remedies.

6. Amendment and Waiver.

Subject to certain exceptions, the Indenture and the Notes may be amended, or default may be waived, with the consent of the Holders of a majority in principal amount of the outstanding Notes. Without notice to or the consent of any Holder, the Company and the Trustee may amend or supplement the Indenture or the Notes to, among other things, cure any ambiguity, defect or inconsistency; provided any such action shall not adversely affect the interests of the Holders of Outstanding Debt Securities.

7. Authentication.

This Note is not valid until the Trustee (or Authenticating Agent) signs the certificate of authentication on the signature page of this Note.

8. Governing Law.

This Note shall be governed by, and construed in accordance with, the laws of the State of New York, without giving effect to its conflicts of laws principles.

9. Abbreviations.

Customary abbreviations may be used in the name of a Holder or an assignee, such as: TEN COM (= tenants in common), TEN ENT (= tenants by the entireties), JT TEN (= joint tenants with right of survivorship and not as tenants in common), CUST (= Custodian) and U/G/M/A/ (= Uniform Gifts to Minors Act).

The Company will furnish a copy of the Indenture to any Holder upon written request and without charge.

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IN WITNESS WHEREOF, the Company has caused this Note to be signed manually or by facsimile by one of its duly authorized officers.

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Sigma-Aldrich Corporation

3.375% Notes due November 1, 2020

[FORM OF TRANSFER NOTICE]

FOR VALUE RECEIVED the undersigned registered holder hereby sell(s), assign(s) and transfer(s) unto:                                              

(Insert Taxpayer Identification No.)                                                                                                                                                                                                 

(Please print or typewrite name and address including zip code of assignee)

the within Note and all rights thereunder, hereby irrevocably constituting and appointing                                                                          

attorney to transfer said Note on the books of the Company with full power of substitution in the premises.

To be executed by an executive officer

SCHEDULE OF EXCHANGES OF INTERESTS IN THE GLOBAL NOTE

The following exchanges of a part of this Global Security for Certificated Securities or a part of another Global Security have been made

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