This announcement is neither an offer to purchase nor a
solicitation of an offer to sell Shares (as defined below). The Offer (as
defined below) is being made solely by the Offer to Purchase dated August 4,
2000 and the related Letter of Transmittal, and is being made to holders of
Shares. Purchaser (as defined below) is not aware of any jurisdiction where the
making of the Offer is prohibited by any administrative or judicial action
pursuant to any valid state statute. If Purchaser becomes aware of any valid
state statute prohibiting the making of the Offer or the acceptance of Shares
pursuant thereto, Purchaser will make a good faith effort to comply with such
state statute. If, after such good faith effort, Purchaser cannot comply with
such state statute, the Offer will not be made to (nor will tenders be accepted
from or on behalf of) the holders of Shares in such state. In any jurisdiction
where the securities, blue sky or other laws require the Offer to be made by a
licensed broker or dealer, the Offer shall be deemed to be made on behalf of
Purchaser by Bear, Stearns & Co. Inc. or one or more registered brokers or
dealers licensed under the laws of such jurisdiction.

                      Notice of Offer to Purchase for Cash

                     All Outstanding Shares of Common Stock

          (Including the Associated Preferred Share Purchase Rights)

                                       of

                                  CHIREX INC.

                                       at

                              $31.25 Net Per Share

                                       by

                            COUSIN ACQUISITION, INC.

                     an indirect wholly owned subsidiary of

                                     RHODIA


             COUSIN ACQUISITION, INC., a Delaware corporation ("Purchaser") and
an indirect wholly owned subsidiary of RHODIA, a French corporation ("Parent"),
is offering to purchase all the issued and outstanding shares of common stock,
par value $.01 per share (the "Common Shares"), of CHIREX INC., a Delaware
corporation (the "Company"), together with the associated rights to purchase
preferred shares that are issued pursuant to the Rights Agreement dated as of
March 31, 1997 between the Company and The First National Bank of Boston as
Rights Agent (the "Rights" and, together with the Common Shares, the "Shares"),
for


                                       2

$31.25 per Share, net to the seller in cash, upon the terms and subject to the
conditions set forth in the Offer to Purchase, dated August 4, 2000 (the "Offer
to Purchase"), and in the related Letter of Transmittal (which, together with
the Offer to Purchase and any amendments or supplements thereto, collectively
constitute the "Offer"). Following the Offer, Purchaser intends to effect the
Merger described below.

  THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
       TIME, ON THURSDAY, AUGUST 31, 2000, UNLESS THE OFFER IS EXTENDED.

             The Offer is conditioned upon, among other things, (i) there having
been validly tendered and not withdrawn prior to the expiration of the Offer at
least the number of Shares that, when added to the Shares already owned by
Parent, shall constitute a majority of the then outstanding Shares on a fully
diluted basis (including, without limitation, all Shares issuable upon the
conversion of any convertible securities or upon the exercise of any options,
warrants, or rights) and (ii) any applicable waiting periods under the
Hart-Scott-Rodino Antitrust Improvements Act of 1976, as amended, and the German
Law Against Restraints on Competition, having expired or been terminated prior
to the expiration of the Offer.

             The Offer is being made pursuant to an Agreement and Plan of
Merger, dated as of July 24, 2000 (the "Merger Agreement"), among Parent,
Purchaser and the Company. The Merger Agreement provides that, among other
things, as promptly as practicable after the purchase of Shares pursuant to the
Offer and the satisfaction of the other conditions set forth in the Merger
Agreement and in accordance with relevant provisions of the General Corporation
Law of the State of Delaware ("Delaware Law"), Purchaser will be merged with and
into the Company or, at the election of Parent, the Company will be merged into
Purchaser or another direct or indirect wholly owned subsidiary of Parent (the
"Merger"). As a result of the Merger, the Company will become an indirect wholly
owned subsidiary of Parent. At the effective time of the Merger (the "Effective
Time"), each Share issued and outstanding immediately prior to the Effective
Time (other than Shares held in the treasury of the Company or Shares owned by
Purchaser, Parent or any direct or indirect wholly owned subsidiary of Parent or
of the Company, and other than Shares held by stockholders who shall have
demanded and perfected appraisal rights under Delaware Law) will be canceled and
converted automatically into the right to receive $31.25 in cash, or any higher
price that may be paid per Share in the Offer, without interest.

             The Board of Directors of the Company has unanimously determined
that the Merger Agreement and the transactions contemplated thereby, including
each of the Offer and the Merger, are fair to, and in the best interests of, the
holders of Shares, has approved, adopted and declared advisable the Merger
Agreement and has resolved to recommend that the holders of Shares accept the
Offer and tender their Shares pursuant to the Offer.

             For purposes of the Offer, Purchaser will be deemed to have
accepted for payment (and thereby purchased) Shares validly tendered and not
properly withdrawn as, if and when Purchaser gives oral or written notice to
Wilmington Trust Company (the "Depositary") of Purchaser's acceptance for
payment of such Shares pursuant to the Offer. Upon the terms and


                                       3

subject to the conditions of the Offer and the Merger Agreement, payment for
Shares accepted for payment pursuant to the Offer will be made by deposit of the
purchase price therefor with the Depositary, which will act as agent for
tendering stockholders for the purpose of receiving payments from Purchaser and
transmitting such payments to tendering stockholders whose Shares have been
accepted for payment. Under no circumstances will interest on the purchase price
for Shares be paid, regardless of any delay in making such payment. In all
cases, payment for Shares tendered and accepted for payment pursuant to the
Offer will be made only after timely receipt by the Depositary of (i) the
certificates evidencing such Shares (the "Share Certificates") or
confirmation of a book-entry transfer of such Shares into the Depositary's
account at the Book-Entry Transfer Facility (as defined in Section 2 of the
Offer to Purchase) pursuant to the procedure set forth in Section 3 of the Offer
to Purchase, (ii) the Letter of Transmittal (or a manually signed facsimile
thereof), properly completed and duly executed, with any required signature
guarantees or, in the case of a book-entry transfer, an Agent's Message (as
defined in Section 2 of the Offer to Purchase) and (iii) any other documents
required by the Letter of Transmittal.

             Purchaser expressly reserves the right, in its sole discretion (but
subject to the terms and conditions of the Merger Agreement), at any time and
from time to time, to extend for any reason the period of time during which the
Offer is open, including the occurrence of any condition specified in Section 14
of the Offer to Purchase, by giving oral or written notice of such extension to
the Depositary. Any such extension will be followed as promptly as practicable
by public announcement thereof, such announcement to be made no later than 9:00
a.m., New York City time, on the next business day after the previously
scheduled expiration date of the Offer. During any such extension, all Shares
previously tendered and not withdrawn will remain subject to the Offer and
subject to the right of a tendering stockholder to withdraw such stockholder's
Shares.

             Shares may be withdrawn at any time prior to 12:00 Midnight, New
York City time, on Thursday, August 31, 2000 (or the latest time and date at
which the Offer, if extended by Purchaser, shall expire). For the withdrawal to
be effective, a written or facsimile transmission notice of withdrawal must be
timely received by the Depositary at one of its addresses set forth on the back
cover page of the Offer to Purchase. Any such notice of withdrawal must specify
the name of the person who tendered the Shares to be withdrawn, the number of
Shares to be withdrawn and the name of the registered holder of such Shares, if
different from that of the person who tendered such Shares. If Share
Certificates evidencing Shares to be withdrawn have been delivered or otherwise
identified to the Depositary, then, prior to the physical release of such Share
Certificates, the serial numbers shown on such Share Certificates must be
submitted to the Depositary and the signature(s) on the notice of withdrawal
must be guaranteed by an Eligible Institution (as defined in Section 3 of the
Offer to Purchase), unless such Shares have been tendered for the account of an
Eligible Institution. If Shares have been tendered pursuant to the procedure for
book-entry transfer as set forth in Section 3 of the Offer to Purchase, any
notice of withdrawal must specify the name and number of the account at the
Book-Entry Transfer Facility to be credited with the withdrawn Shares. All
questions as to the form and validity (including the time of receipt) of any
notice of withdrawal will be determined by Purchaser, in its sole discretion,
whose determination will be final and binding.


                                       4

             The information required to be disclosed by Rule 14d-6(d)(1) of the
General Rules and Regulations under the Securities Exchange Act of 1934, as
amended, is contained in the Offer to Purchase and is incorporated herein by
reference.

             The Company has caused its transfer agent to provide Purchaser with
the Company's stockholder list and security position listings for the purpose of
disseminating the Offer to holders of Shares. The Offer to Purchase and the
related Letter of Transmittal will be mailed to record holders of Shares whose
names appear on the Company's stockholder lists and will be furnished to
brokers, dealers, commercial banks, trust companies and similar persons whose
names, or the names of whose nominees, appear on the stockholder list or, if
applicable, who are listed as participants in a clearing agency's security
position listing for subsequent transmittal to beneficial owners of Shares.

             The Offer to Purchase and the related Letter of Transmittal contain
important information which should be read before any decision is made with
respect to the Offer.

             Questions and requests for assistance or for additional copies of
the Offer to Purchase and the related Letter of Transmittal and other tender
offer materials may be directed to the Information Agent or the Dealer Manager
as set forth below, and copies will be furnished promptly at Purchaser's
expense. No fees or commissions will be paid to brokers, dealers or other
persons (other than the Information Agent and the Dealer Manager) for soliciting
tenders of Shares pursuant to the Offer.

                    The Information Agent for the Offer is:

                                   MacKenzie
                                 Partners, Inc.

                                156 Fifth Avenue
                            New York, New York 10010
                         (212) 929-5500 (Call Collect)
                                       or
                         Call Toll-Free (800) 322-2885


                      The Dealer Manager for the Offer is:

                           Bear, Stearns & Co. Inc.

                                245 Park Avenue
                            New York, New York 10167

                         Call Toll-Free (877) 850-8074

August 4, 2000